Prepare Data for Machine Processing

Scaling

You can scale the values within a column using either of the following techniques.

Scale to zero mean and unit variance

Zero mean and unit variance scaling renders the values in the set to fit a normal distribution with a mean of 0 and a variance of 1. This technique is a common standard for normalizing values into a normal distribution for statistical purposes.

In the following example, the values in the POS_Sales column have been normalized to average 0, variance 1. 

• Remove mean: When selected, the existing mean (average) of the values is used as the center of the distribution curve.
  
  

  NOTE: Re-centering sparse data by removing the mean may remove sparseness.

• Scale to unit variance: When selected, the range of values are scaled such that their variance is 1. When deselected, the existing variance is maintained.

  NOTE: Scaling to unit variance may not work well for managing outliers. Some additional techniques for managing outliers are outlined below.

Scale to min-max range

You can scale column values fitting between a specified minimum and maximum value. This technique is useful for distributions with very small standard deviation values and for preserving 0 values in sparse data.

The following example scales the TestScores column to a range of 0 and 1, inclusive.

Outliers

You can use several techniques for identifying statistical outliers in your dataset and managing them as needed.

Identify outliers

Suppose you need to remove the outliers from a column. Assuming a normal bell distribution of values, you can use the following formula to calculate the number of standard deviations a column value is from the column mean (average). In this case, the source column is POS_Sales.

Remove outliers

The new stdevs_POS_Sales column now contains the number of standard deviations from the mean for the corresponding value in POS_Sales. You can use the following transformation to remove the rows that contain outlier values for this column.

In the following transformation, all rows that contain a value in POS_Sales that is greater than four standard deviations from the mean are deleted:

Change outliers to mean values

You can also remove the effects of outliers be setting their value to the mean (average), which preserves the data in other columns in the row. 

Binning

You can modify your data to fit into bins of equal or custom size. For example, the lowest values in your range would be marked in the 0 bin, with larger values being marked with larger bin numbers.

Bins of equal size

You can bin numeric values into bins of equal size. Suppose your column contains numeric values 0-1000. You can bin values into equal ranges of 100 by creating 10 bins.

Bins of custom size

You can also create custom bins. In the following example, the TestScores column is binned into the following bins. In a later step, these bins are mapped to grades:

First, you bin values into the bin numbers listed above: 

You can then use the following transformation to assign letters in the Grades column:

One-Hot Encoding

One-hot encoding refers to distributing the listed values in a column into individual columns. Within each row of each individual column is a 0 or a 1, depending on whether the value represented by the column appears in the corresponding source column. The source column is untouched. This method of encoding allows for easier consumption of data in target systems.

In the following example, the values in the BrandName column are distributed into separate columns of binary values, with a maximum limit of 50 new columns.