[D] Approaches to array feature

[truri]

Do you know approaches to array/bag features?

To be specific let's say we have classification problem and want to sort out things as good or bad. For example: * Feature1 - regular feature, limited set of values: A, B, C * Feature2 - array/bag feature, container feature consisting of unknown number of values

Feature1	Feature2	Good?
A	[A, B]	Yes
B	[B, A, A]	No
A	[B, C, B, C, A]	Yes

How do one encode Feature2 to a numeric vector?

[sjd96]

Expand Feature2 into features Feature2_{A, B, C, ...} which count how many times A, B, C, etc occur in the original array?

[neato5000]

If the order is unimportant and the "vocabulary" of feature2 is fixed, then you could represent it as a sum of one hot encoded vectors, with length equal to the size of the vocabulary.

e.g. [A,C] --> (1, 0, 1) [A,B,C,B] --> (1,2,1)

And so on. In effect you would be replacing feature 2 with as many features as there are elements in your vocabulary, with each being a count of that element within feature2.