How to use Data Scaling Improve Deep Learning Model Stability and Performance

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Deep learning neural networks learn how to map inputs to outputs from examples in a training dataset.

The weights of the model are initialized to small random values and updated via an optimization algorithm in response to estimates of error on the training dataset.

Given the use of small weights in the model and the use of error between predictions and expected values, the scale of inputs and outputs used to train the model are an important factor. Unscaled input variables can result in a slow or unstable learning process, whereas unscaled target variables on regression problems can result in exploding gradients causing the learning process to fail.

Data preparation involves using techniques such as the normalization and standardization to rescale input and output variables prior to training a neural network model.

In this tutorial, you will discover how to improve neural network stability and modeling performance by scaling data.

After completing this tutorial, you will know:

  • Data scaling is a recommended pre-processing step when working with deep learning neural networks.
  • Data scaling can be achieved by normalizing or standardizing real-valued input and output variables.
  • How to apply standardization and normalization to improve the performance of a Multilayer Perceptron model on a regression predictive modeling problem.

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How to Improve Neural Network Stability and Modeling Performance With Data Scaling

How to Improve Neural Network Stability and Modeling Performance With Data Scaling
Photo by Javier Sanchez Portero, some rights reserved.

Tutorial Overview

This tutorial is divided into six parts; they are:

  1. The Scale of Your Data Matters
  2. Data Scaling Methods
  3. Regression Predictive Modeling Problem
  4. Multilayer Perceptron With Unscaled Data
  5. Multilayer Perceptron With Scaled Output Variables
  6. Multilayer Perceptron With Scaled Input Variables

The Scale of Your Data Matters

Deep learning neural network models learn a mapping from input variables to an output variable.

As such, the scale and distribution of the data drawn from the domain may be different for each variable.

Input variables may have different units (e.g. feet, kilometers, and hours) that, in turn, may mean the variables have different scales.

Differences in the scales across input variables may increase the difficulty of the problem being modeled. An example of this is that large input values (e.g. a spread of hundreds or thousands of units) can result in a model that learns large weight values. A model with large weight values is often unstable, meaning that it may suffer from poor performance during learning and sensitivity to input values resulting in higher generalization error.

One of the most common forms of pre-processing consists of a simple linear rescaling of the input variables.

— Page 298, Neural Networks for Pattern Recognition, 1995.

A target variable with a large spread of values, in turn, may result in large error gradient values causing weight values to change dramatically, making the learning process unstable.

Scaling input and output variables is a critical step in using neural network models.

In practice it is nearly always advantageous to apply pre-processing transformations to the input data before it is presented to a network. Similarly, the outputs of the network are often post-processed to give the required output values.

— Page 296, Neural Networks for Pattern Recognition, 1995.

Scaling Input Variables

The input variables are those that the network takes on the input or visible layer in order to make a prediction.

A good rule of thumb is that input variables should be small values, probably in the range of 0-1 or standardized with a zero mean and a standard deviation of one.

Whether input variables require scaling depends on the specifics of your problem and of each variable.

You may have a sequence of quantities as inputs, such as prices or temperatures.

If the distribution of the quantity is normal, then it should be standardized, otherwise the data should be normalized. This applies if the range of quantity values is large (10s, 100s, etc.) or small (0.01, 0.0001).

If the quantity values are small (near 0-1) and the distribution is limited (e.g. standard deviation near 1) then perhaps you can get away with no scaling of the data.

Problems can be complex and it may not be clear how to best scale input data.

If in doubt, normalize the input sequence. If you have the resources, explore modeling with the raw data, standardized data, and normalized data and see if there is a beneficial difference in the performance of the resulting model.

If the input variables are combined linearly, as in an MLP [Multilayer Perceptron], then it is rarely strictly necessary to standardize the inputs, at least in theory. […] However, there are a variety of practical reasons why standardizing the inputs can make training faster and reduce the chances of getting stuck in local optima.

Should I normalize/standardize/rescale the data? Neural Nets FAQ

Scaling Output Variables

The output variable is the variable predicted by the network.

You must ensure that the scale of your output variable matches the scale of the activation function (transfer function) on the output layer of your network.

If your output activation function has a range of [0,1], then obviously you must ensure that the target values lie within that range. But it is generally better to choose an output activation function suited to the distribution of the targets than to force your data to conform to the output activation function.

Should I normalize/standardize/rescale the data? Neural Nets FAQ

If your problem is a regression problem, then the output will be a real value.

This is best modeled with a linear activation function. If the distribution of the value is normal, then you can standardize the output variable. Otherwise, the output variable can be normalized.

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Data Scaling Methods

There are two types of scaling of your data that you may want to consider: normalization and standardization.

These can both be achieved using the scikit-learn library.

Data Normalization

Normalization is a rescaling of the data from the original range so that all values are within the range of 0 and 1.

Normalization requires that you know or are able to accurately estimate the minimum and maximum observable values. You may be able to estimate these values from your available data.

A value is normalized as follows:

Where the minimum and maximum values pertain to the value x being normalized.

For example, for a dataset, we could guesstimate the min and max observable values as 30 and -10. We can then normalize any value, like 18.8, as follows:

You can see that if an x value is provided that is outside the bounds of the minimum and maximum values, the resulting value will not be in the range of 0 and 1. You could check for these observations prior to making predictions and either remove them from the dataset or limit them to the pre-defined maximum or minimum values.

You can normalize your dataset using the scikit-learn object MinMaxScaler.

Good practice usage with the MinMaxScaler and other scaling techniques is as follows:

  • Fit the scaler using available training data. For normalization, this means the training data will be used to estimate the minimum and maximum observable values. This is done by calling the fit() function.
  • Apply the scale to training data. This means you can use the normalized data to train your model. This is done by calling the transform() function.
  • Apply the scale to data going forward. This means you can prepare new data in the future on which you want to make predictions.

The default scale for the MinMaxScaler is to rescale variables into the range [0,1], although a preferred scale can be specified via the “feature_range” argument and specify a tuple including the min and the max for all variables.

If needed, the transform can be inverted. This is useful for converting predictions back into their original scale for reporting or plotting. This can be done by calling the inverse_transform() function.

The example below provides a general demonstration for using the MinMaxScaler to normalize data.

You can also perform the fit and transform in a single step using the fit_transform() function; for example:

Data Standardization

Standardizing a dataset involves rescaling the distribution of values so that the mean of observed values is 0 and the standard deviation is 1. It is sometimes referred to as “whitening.”

This can be thought of as subtracting the mean value or centering the data.

Like normalization, standardization can be useful, and even required in some machine learning algorithms when your data has input values with differing scales.

Standardization assumes that your observations fit a Gaussian distribution (bell curve) with a well behaved mean and standard deviation. You can still standardize your data if this expectation is not met, but you may not get reliable results.

Standardization requires that you know or are able to accurately estimate the mean and standard deviation of observable values. You may be able to estimate these values from your training data.

A value is standardized as follows:

Where the mean is calculated as:

And the standard_deviation is calculated as:

We can guesstimate a mean of 10 and a standard deviation of about 5. Using these values, we can standardize the first value of 20.7 as follows:

The mean and standard deviation estimates of a dataset can be more robust to new data than the minimum and maximum.

You can standardize your dataset using the scikit-learn object StandardScaler.

You can also perform the fit and transform in a single step using the fit_transform() function; for example:

Regression Predictive Modeling Problem

A regression predictive modeling problem involves predicting a real-valued quantity.

We can use a standard regression problem generator provided by the scikit-learn library in the make_regression() function. This function will generate examples from a simple regression problem with a given number of input variables, statistical noise, and other properties.

We will use this function to define a problem that has 20 input features; 10 of the features will be meaningful and 10 will not be relevant. A total of 1,000 examples will be randomly generated. The pseudorandom number generator will be fixed to ensure that we get the same 1,000 examples each time the code is run.

Each input variable has a Gaussian distribution, as does the target variable.

We can demonstrate this by creating histograms of some of the input variables and the output variable.

Running the example creates two figures.

The first shows histograms of the first two of the twenty input variables, showing that each has a Gaussian data distribution.

Histograms of Two of the Twenty Input Variables for the Regression Problem

Histograms of Two of the Twenty Input Variables for the Regression Problem

The second figure shows a histogram of the target variable, showing a much larger range for the variable as compared to the input variables and, again, a Gaussian data distribution.

Histogram of the Target Variable for the Regression Problem

Histogram of the Target Variable for the Regression Problem

Now that we have a regression problem that we can use as the basis for the investigation, we can develop a model to address it.

Multilayer Perceptron With Unscaled Data

We can develop a Multilayer Perceptron (MLP) model for the regression problem.

A model will be demonstrated on the raw data, without any scaling of the input or output variables. We expect that model performance will be generally poor.

The first step is to split the data into train and test sets so that we can fit and evaluate a model. We will generate 1,000 examples from the domain and split the dataset in half, using 500 examples for the train and test datasets.

Next, we can define an MLP model. The model will expect 20 inputs in the 20 input variables in the problem.

A single hidden layer will be used with 25 nodes and a rectified linear activation function. The output layer has one node for the single target variable and a linear activation function to predict real values directly.

The mean squared error loss function will be used to optimize the model and the stochastic gradient descent optimization algorithm will be used with the sensible default configuration of a learning rate of 0.01 and a momentum of 0.9.

The model will be fit for 100 training epochs and the test set will be used as a validation set, evaluated at the end of each training epoch.

The mean squared error is calculated on the train and test datasets at the end of training to get an idea of how well the model learned the problem.

Finally, learning curves of mean squared error on the train and test sets at the end of each training epoch are graphed using line plots, providing learning curves to get an idea of the dynamics of the model while learning the problem.

Tying these elements together, the complete example is listed below.

Running the example fits the model and calculates the mean squared error on the train and test sets.

In this case, the model is unable to learn the problem, resulting in predictions of NaN values. The model weights exploded during training given the very large errors and, in turn, error gradients calculated for weight updates.

This demonstrates that, at the very least, some data scaling is required for the target variable.

A line plot of training history is created but does not show anything as the model almost immediately results in a NaN mean squared error.

Multilayer Perceptron With Scaled Output Variables

The MLP model can be updated to scale the target variable.

Reducing the scale of the target variable will, in turn, reduce the size of the gradient used to update the weights and result in a more stable model and training process.

Given the Gaussian distribution of the target variable, a natural method for rescaling the variable would be to standardize the variable. This requires estimating the mean and standard deviation of the variable and using these estimates to perform the rescaling.

It is best practice is to estimate the mean and standard deviation of the training dataset and use these variables to scale the train and test dataset. This is to avoid any data leakage during the model evaluation process.

The scikit-learn transformers expect input data to be matrices of rows and columns, therefore the 1D arrays for the target variable will have to be reshaped into 2D arrays prior to the transforms.

We can then create and apply the StandardScaler to rescale the target variable.

Rescaling the target variable means that estimating the performance of the model and plotting the learning curves will calculate an MSE in squared units of the scaled variable rather than squared units of the original scale. This can make interpreting the error within the context of the domain challenging.

In practice, it may be helpful to estimate the performance of the model by first inverting the transform on the test dataset target variable and on the model predictions and estimating model performance using the root mean squared error on the unscaled data. This is left as an exercise to the reader.

The complete example of standardizing the target variable for the MLP on the regression problem is listed below.

Running the example fits the model and calculates the mean squared error on the train and test sets.

Your specific results may vary given the stochastic nature of the learning algorithm. Try running the example a few times.

In this case, the model does appear to learn the problem and achieves near-zero mean squared error, at least to three decimal places.

A line plot of the mean squared error on the train (blue) and test (orange) dataset over each training epoch is created.

In this case, we can see that the model rapidly learns to effectively map inputs to outputs for the regression problem and achieves good performance on both datasets over the course of the run, neither overfitting or underfitting the training dataset.

Line Plot of Mean Squared Error on the Train a Test Datasets for Each Training Epoch

Line Plot of Mean Squared Error on the Train a Test Datasets for Each Training Epoch

It may be interesting to repeat this experiment and normalize the target variable instead and compare results.

Multilayer Perceptron With Scaled Input Variables

We have seen that data scaling can stabilize the training process when fitting a model for regression with a target variable that has a wide spread.

It is also possible to improve the stability and performance of the model by scaling the input variables.

In this section, we will design an experiment to compare the performance of different scaling methods for the input variables.

The input variables also have a Gaussian data distribution, like the target variable, therefore we would expect that standardizing the data would be the best approach. This is not always the case.

We can compare the performance of the unscaled input variables to models fit with either standardized and normalized input variables.

The first step is to define a function to create the same 1,000 data samples, split them into train and test sets, and apply the data scaling methods specified via input arguments. The get_dataset() function below implements this, requiring the scaler to be provided for the input and target variables and returns the train and test datasets split into input and output components ready to train and evaluate a model.

Next, we can define a function to fit an MLP model on a given dataset and return the mean squared error for the fit model on the test dataset.

The evaluate_model() function below implements this behavior.

Neural networks are trained using a stochastic learning algorithm. This means that the same model fit on the same data may result in a different performance.

We can address this in our experiment by repeating the evaluation of each model configuration, in this case a choice of data scaling, multiple times and report performance as the mean of the error scores across all of the runs. We will repeat each run 30 times to ensure the mean is statistically robust.

The repeated_evaluation() function below implements this, taking the scaler for input and output variables as arguments, evaluating a model 30 times with those scalers, printing error scores along the way, and returning a list of the calculated error scores from each run.

Finally, we can run the experiment and evaluate the same model on the same dataset three different ways:

  • No scaling of inputs, standardized outputs.
  • Normalized inputs, standardized outputs.
  • Standardized inputs, standardized outputs.

The mean and standard deviation of the error for each configuration is reported, then box and whisker plots are created to summarize the error scores for each configuration.

Tying these elements together, the complete example is listed below.

Running the example prints the mean squared error for each model run along the way.

After each of the three configurations have been evaluated 30 times each, the mean errors for each are reported.

Your specific results may vary, but the general trend should be the same as is listed below.

In this case, we can see that as we expected, scaling the input variables does result in a model with better performance. Unexpectedly, better performance is seen using normalized inputs instead of standardized inputs. This may be related to the choice of the rectified linear activation function in the first hidden layer.

A figure with three box and whisker plots is created summarizing the spread of error scores for each configuration.

The plots show that there was little difference between the distributions of error scores for the unscaled and standardized input variables, and that the normalized input variables result in better performance and more stable or a tighter distribution of error scores.

These results highlight that it is important to actually experiment and confirm the results of data scaling methods rather than assuming that a given data preparation scheme will work best based on the observed distribution of the data.

Box and Whisker Plots of Mean Squared Error With Unscaled, Normalized and Standardized Input Variables for the Regression Problem

Box and Whisker Plots of Mean Squared Error With Unscaled, Normalized and Standardized Input Variables for the Regression Problem

Extensions

This section lists some ideas for extending the tutorial that you may wish to explore.

  • Normalize Target Variable. Update the example and normalize instead of standardize the target variable and compare results.
  • Compared Scaling for Target Variable. Update the example to compare standardizing and normalizing the target variable using repeated experiments and compare the results.
  • Other Scales. Update the example to evaluate other min/max scales when normalizing and compare performance, e.g. [-1, 1] and [0.0, 0.5].

If you explore any of these extensions, I’d love to know.

Further Reading

This section provides more resources on the topic if you are looking to go deeper.

Posts

Books

API

Articles

Summary

In this tutorial, you discovered how to improve neural network stability and modeling performance by scaling data.

Specifically, you learned:

  • Data scaling is a recommended pre-processing step when working with deep learning neural networks.
  • Data scaling can be achieved by normalizing or standardizing real-valued input and output variables.
  • How to apply standardization and normalization to improve the performance of a Multilayer Perceptron model on a regression predictive modeling problem.

Do you have any questions?
Ask your questions in the comments below and I will do my best to answer.

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47 Responses to How to use Data Scaling Improve Deep Learning Model Stability and Performance

  1. Wonbin February 13, 2019 at 6:03 pm #

    Thank you for this helpful post for beginners!

    Could you please provide more details about the steps of “using the root mean squared error on the unscaled data” to interpret the performance in a specific domain?

    Would it be like this??
    ———————————————————–
    1. Finalize the model (based on the performance being calculated from the scaled output variable)
    2. Make predictions on test set
    3. Invert the predictions (to convert them back into their original scale)
    4. Calculate the metrics (e.g. RMSE, MAPE)
    ———————————————————–

    Waiting for your reply! Cheers mate!

    • Jason Brownlee February 14, 2019 at 8:39 am #

      Correct.

    • ajebulon April 30, 2019 at 2:44 pm #

      Really nice article! I got Some quick questions,

      If I have multiple input columns, each has different value range, might be [0, 1000] or even a one-hot-encoded data, should all be scaled with same method, or it can be processed differently?

      For example:
      – input A is normalized to [0, 1],
      – input B is normalized to [-1, 1],
      – input C is standardized,
      – one-hot-encoded data is not scaled

      • Jason Brownlee May 1, 2019 at 6:58 am #

        Yes, typically it is a good idea to scale all columns to have the same range. Perhaps start with [0,1] and compare others to see if they result in an improvement.

  2. mk123qwe February 19, 2019 at 5:38 pm #

    we want standardized inputs, no scaling of outputs,but outputs value is not in (0,1).Are the predictions inaccurate?

    • Jason Brownlee February 20, 2019 at 7:51 am #

      I don’t follow, are what predictions accurate?

  3. yingxiao kong February 28, 2019 at 8:17 am #

    Hi Jason,

    Your experiment is very helpful for me to understand the difference between different methods, actually I have also done similar things. I always standardized the input data. I have compared the results between standardized and standardized targets. The plots shows that with standardized targets, the network seems to work better. However, here I have a question: suppose the standard deviation of my target is 300, then I think the MSE will be strongly decreased after you fixed the standard deviation to 1. So shall we multiply the original std to the MSE in order to get the MSE in the original target value space?

  4. Beato March 11, 2019 at 3:51 am #

    Hi Jason,

    My data includes categorical and continued data. Could I transform the categorical data with 1,2,3…into standardized data and put them into the neural network models to make classification? Or do I need to transformr the categorical data with with one-hot coding(0,1)? I have been confused about it. Thanks

  5. Bart March 16, 2019 at 5:23 am #

    Hi Jason, I have a specific Question regarding the normalization (min-max scaling) of the output value. Usually you are supposed to use normalization only on the training data set and then apply those stats to the validation and test set. Otherwise you would feed the model at training time certain information about the world it shouldn’t have access to. (The Elements of Statistical Learning: Data Mining, Inference, and Prediction p.247)

    But for instance, my output value is a single percentage value ranging [0, 100%] and I am using the ReLU activation function in my output layer. I know for sure that in the “real world” regarding my problem statement, that I will get samples ranging form 60 – 100%. But my training sample size is to small and does not contain enough data points including all possible output values. So here comes my question: Should I stay with my initial statement (normalization only on training data set) or should I apply the maximum possible value of 100% to max()-value of the normalization step? The latter would contradict the literature. Best Regards Bart

    • Jason Brownlee March 16, 2019 at 8:02 am #

      Correct.

      I would recommend a sigmoid activation in the output.

      I would then recommend interpreting the 0-1 scale as 60-100 prior to model evaluation.

      Does that help?

      • Bart March 17, 2019 at 1:37 am #

        I’m not quite sure what you mean by your second recommendation. How would I achieve that?

        • Jason Brownlee March 17, 2019 at 6:24 am #

          You can project the scale of 0-1 to anything you want, such as 60-100.

          First rescale to a number between 0 and 40 (value * 40) then add the min value (+ 60)

          result = value * 40 + 60

  6. Mike March 25, 2019 at 1:04 am #

    Dear Jason, thank you for the great article.

    I am wondering if there is any advantage using StadardScaler or MinMaxScaler over scaling manually. I could calculate the mean, std or min, max of my training data and apply them with the corresponding formula for standard or minmax scaling.

    Would this approach produce the same results as the StadardScaler or MinMaxScaler or are the sklearn scalers special?

    • Jason Brownlee March 25, 2019 at 6:46 am #

      Yes, it is reliable bug free code all wrapped up in a single class – making it harder to introduce new bugs.

      Same results as manual, if you coded the manual scaling correctly.

  7. Magnus May 9, 2019 at 8:32 pm #

    Dear Jason,

    I have a few questions from section “Data normalization”. You mention that we should estimate the max and min values, and use that to normalize the training set to e.g. [-1,1]. But what if the max and min values are in the validation or test set? Then I might get values e.g. [-1.2, 1.3] in the validation set. Do you consider this to be incorrect or not?

    Another approach is then to make sure that the min and max values for all parameters are contained in the training set. What are your thoughts on this? Is this the way to do it? Or should we use the max and min values for all data combined (training, validation and test sets) when normalizing the training set?

    For the moment I use the MinMaxScaler and fit_transform on the training set and then apply that scaler on the validation and test set using transform. But I realise that some of my max values are in the validation set. I suppose this is also related to network saturation.

    • Jason Brownlee May 10, 2019 at 8:16 am #

      Perhaps estimate the min/max using domain knowledge. If new data exceeded the limits, snap to known limits, or not – test and see how the model is impacted.

      Regardless, the training set must be representative of the problem.

  8. youssef May 30, 2019 at 9:33 am #

    Hello Jason, I am a huge fan of your work! Thank you so much for your insightful tutorials. You are a life saver! I have a small question if i may:

    I am trying to fit spectrograms in a cnn in order to do some classification tasks. Unfortunately each spectrogram is around (3000,300) array. Is there a way to reduce the dimensionality without losing so much information?

    • Jason Brownlee May 30, 2019 at 2:50 pm #

      Ouch, perhaps start with simple downsampling and see what effect that has?

  9. Muktamani July 4, 2019 at 8:54 pm #

    Hi Jason,
    It was always good and informative to go through your blogs and your interaction with comments by different people all across the globe.
    I have question regarding the scaling techniques.

    As you explained about scaling :
    Case1:
    # created scaler
    scaler = StandardScaler()
    # fit scaler on training dataset
    scaler.fit(trainy)
    # transform training dataset
    trainy = scaler.transform(trainy)
    # transform test dataset
    testy = scaler.transform(testy)

    in this case mean and standard deviation for all train and test remain same.

    What i approached is:
    case2
    # created scaler
    scaler_train = StandardScaler()
    # fit scaler on training dataset
    scaler_train.fit(trainy)
    # transform training dataset
    trainy = scaler_train.transform(trainy)

    # created scaler
    scaler_test = StandardScaler()
    # fit scaler on training dataset
    scaler_test.fit(trainy)
    # transform test dataset
    testy = scaler_test.transform(testy)

    Here the mean and standard deviation in train data and test data are different.so model may find the test data completely unknown and new .rather in first case where mean and standard deviation is same on train and test data that may leads to providing the known test data to model (known in term of same mean and standard deviation treatment).

    Jason,can you guide me if my logics is good to go with case2 or shall i consider case1 .
    or if logic is wrong you can also say that and explain.
    (Also i applied Same for min-max scaling i.e normalization, if i choose this then)
    Again thanks Jason for such a nice work !

    Happy Learning !!

    • Jason Brownlee July 5, 2019 at 8:06 am #

      I recommend fitting the scaler on the training dataset once, then apply it to transform the training dataset and test set.

      If you fit the scaler using the test dataset, you will have data leakage and possibly an invalid estimate of model performance.

  10. ICHaLiL July 6, 2019 at 12:13 am #

    Hi Jason,

    I’m working on sequence2sequence problem. Input’s max and min points are around 500-300, however output’s are 200-0. If I want to normalize them, should I use different scalers? For example:

    scx = MinMaxScaler(feature_range = (0, 1))
    scy = MinMaxScaler(feature_range = (0, 1))

    trainx = scx.fit_transform(trainx)
    trainy = scy.fit_transform(trainy)

    or should I scale them with same scale like below?

    sc = MinMaxScaler(feature_range = (0, 1))

    trainx = sc.fit_transform(trainx)
    trainy = sc.fit_transform(trainy)

    • Jason Brownlee July 6, 2019 at 8:40 am #

      Yes, use a separate transform for inputs and outputs is a good idea. Otherwise have them all as separate columns in the same matrix and use one scaler, but the column order for transform/inverse_transform will always have to be consistent.

  11. Brent July 12, 2019 at 6:55 pm #

    Hi Jason,

    Confused about one aspect, I have a small NN with 8 independent variables and one dichotomous dependent variable. I have standardized the input variables (the output variable was left untouched). I have both trained and created the final model with the same standardized data. However, the question is, if I want to create a user interface to receive manual inputs, those will no longer be in the standardized format, so what is the best way to proceed?

    • Jason Brownlee July 13, 2019 at 6:53 am #

      You must maintain the objects used to prepare the data, or the coefficients used by those objects (mean and stdev) so that you can prepare new data in an identically way to the way data was prepared during training.

      Does that help

      • Brent July 15, 2019 at 10:58 am #

        Thank you, that makes perfect sense.

  12. cgv July 21, 2019 at 11:27 pm #

    Hi Jason,

    I have built an ANN model and scaled my inputs and outputs before feeding to the network. I measure the performance of the model by r2_score. My output variable is height. My r2_score when the output variable is in metres is .98, but when my output variable is in centi-metres , my r2_score is .91. I have scaled my output too before feeding to the network, why is there a difference in r2_score even because the output variable is scaled before feeding to the network.

    Thanks in advance

    • Jason Brownlee July 22, 2019 at 8:27 am #

      Good question, this is why it is important to test different scaling approaches in order to discover what works best for a given dataset and model combination.

    • madhuri August 29, 2019 at 3:44 am #

      Hi Jason,
      I am working on sequence to data prediction problem wherein i am performing normalization on input and output both.
      Once model is trained then to get the actual output in real-time, I have to perform the de-normalization and when I will perform the denorm then error will increase by the same factor I have used for normalization.
      Lets consider, norm predicted output is 0.1 and error of the model is 0.01 .
      denorm predicted output become 0.1*100 = 10 and after de-normalizing the error will be 0.01*100= 1
      So, what will be solution to this eliminate this kind of problem in regression.

      Thanks

      • Jason Brownlee August 29, 2019 at 6:16 am #

        What problem exactly?

        • madhuri August 29, 2019 at 8:38 pm #

          The problem is after de-normalization of the output, the error difference between actual and predicted output is scaled up by the normalization factor (max-min) So, I want to know what can be done to make the error difference same for both de-normized as well as normalized output.

          Thanks

  13. joshBorrison October 7, 2019 at 5:08 pm #

    Hi Jason,

    Do I have to use only one normalization formula for all inputs?

    For example: I have 5 inputs [inp1, inp2, inp3, inp4, inp5] where I can estimate max and min only for [inp1, inp2]. So can I use

    y = (x – min) / (max – min)

    for [inp1, inp2] and

    y = x/(1+x)

    for [inp3, inp4, inp5]?

    • Jason Brownlee October 8, 2019 at 7:53 am #

      Yes, it is applied to each input separately – assuming they have different units.

  14. shiva November 13, 2019 at 4:17 am #

    Hi Jason

    what if I scale the word vectors(glove) for exposing to LSTM?

    would it affect the accuracy of results or it maintains the semantic relations of words?

    Thank you a lot.

  15. Murilo Souza November 14, 2019 at 12:35 am #

    Hello, i was trying to normalize/inverse transoformation in my data, but i got one error that i think its due to the resize i did in my input data. Here’s my code:

    import numpy as np
    import tensorflow as tf
    from tensorflow import keras
    import pandas as pd
    import time as time
    import matplotlib.pyplot as plt
    import pydot
    import csv as csv
    import keras.backend as K
    from sklearn.preprocessing import MinMaxScaler

    # Downloading data
    !wget https://raw.githubusercontent.com/sibyjackgrove/CNN-on-Wind-Power-Data/master/MISO_power_data_classification_labels.csv
    !wget https://raw.githubusercontent.com/sibyjackgrove/CNN-on-Wind-Power-Data/master/MISO_power_data_input.csv

    # Trying normalization
    batch_size = 1
    valid_size = max(1,np.int(0.2*batch_size))
    df_input = pd.read_csv(‘./MISO_power_data_input.csv’,usecols =[‘Wind_MWh’,’Actual_Load_MWh’], chunksize=24*(batch_size+valid_size),nrows = 24*(batch_size+valid_size),iterator=True)
    df_target = pd.read_csv(‘./MISO_power_data_classification_labels.csv’,usecols =[‘Mean Wind Power’,’Standard Deviation’,’WindShare’],chunksize =batch_size+valid_size,nrows = batch_size+valid_size, iterator=True)
    for chunk, chunk2 in zip(df_input,df_target):
    InputX = chunk.values
    InputX = np.resize(InputX,(batch_size+valid_size,24,2,1))
    print(InputX)
    InputX.astype(‘float32’, copy=False)
    InputY = chunk2.values
    InputY.astype(‘float32’, copy=False)
    print(InputY)

    # create scaler
    scaler = MinMaxScaler() # Define limits for normalize data
    normalized_input = scaler.fit_transform(InputX) # Normalize input data
    normalized_output = scaler.fit_transform(InputY) # Normalize output data
    print(normalized_input)
    print(normalized_output)
    inverse_output = scaler.inverse_transform(normalized_output) # Inverse transformation of output data
    print(inverse_output)

    The error:

    “ValueError: Found array with dim 4. MinMaxScaler expected <= 2."

    Do you have any idea how can i fix this? I really didn't wish to change the resize command at the moment.

  16. Jules Damji November 14, 2019 at 6:55 am #

    Hey Jason,

    I love this tutorial. I was wondering if I can get your permission to use this tutorial, convert all its experimentation and tracking using MLflow, and include it in my tutorials I teach at conferences.

    It’s a fitting example of how you can use MLFlow to track different experiments and visually compare the outcomes.

    All the credit will be given to you as the source and inspiration. You can see some of the examples here: https://github.com/dmatrix/spark-saturday/tree/master/tutorials/mlflow/src/python.

    • Jason Brownlee November 14, 2019 at 8:07 am #

      Thanks!

      No problem as long as you clearly cite and link to the post.

  17. jules Damji November 14, 2019 at 2:45 pm #

    Thanks, I will certainly put the original link and plug your book too, along with your site and an excellent resource of tutorials and examples to learn from.

    Cheers
    Jules

  18. Hanser November 28, 2019 at 8:13 am #

    Amazing content Jason! I was wondering if it is possible to apply different scalers to different inputs given based on their original characteristics? I am asking you that because as you mentioned in the tutorial “Differences in the scales across input variables may increase the difficulty of the problem being modeled” Therefore, if I use standard scaler in one input and normal scaler in another it could be bad for gradient descend.

    • Jason Brownlee November 28, 2019 at 8:16 am #

      Thanks!

      Yes, perhaps try it and compare the results to using one type of scaling for all inputs.

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