HiveMall: Transform Categorical features to Numerical

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HiveMall is a machine learning library that sits on top of Hive and provides SQL interface to wide range of data preparation and machine learning algorithms.

A common task faced for many machine learning exercises is to convert the data from the format it is captured in (raw data) into a format that is required by the machine learning algorithms. Most ML tools will either have functionality built into the algorithms to do this automatically or will provide functions to allow you to manage this process yourself.

In HiveMall we have the ‘quantified_features’ function and is used for transforming values of non-number columns to indexed numbers, but it does have some unusual but useful features.

In this example I’ll use the titanic data set to illustrate the usage of this feature.

Screenshot 2019-04-29 15.14.42

Here we have a mixture of features with categorical and numerical.

select 
  quantified_features(
    ${output_row}, PassengerId, Survived, Pclass, Sex, Age, SibSp, Parch, Fare, Cabin, Embarked) as features
from (
  select * from titanic
  order by Passengerid asc
) t
limit 5;

and we get the following output

[1.0,0.0,0.0,3.0,0.0,22.0,1.0,0.0,7.25,0.0,1.0]
[2.0,1.0,1.0,1.0,1.0,38.0,1.0,0.0,71.2833,1.0,2.0]
[3.0,1.0,1.0,3.0,1.0,26.0,0.0,0.0,7.9250,0.0,1.0]
[4.0,1.0,1.0,1.0,1.0,35.0,1.0,0.0,53.1,3.0,1.0]
[5.0,1.0,0.0,3.0,0.0,35.0,0.0,0.0,8.05,0.0,1.0]

The ordering within the attributes is important, and some thinking is needed if there is a defined order and you want this reflected in the outputs of the transformed features

If you are a numeric field that you want treated as a categorical, and transformed, you can cast it into a string

e.g.

cast(SibSp as string)
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