如何将 dataframe 转换为 0 和 1 的 ndarray？

Question

I have a Pandas dataframe which looks like this:

col_1 col_2
a     4
a     3
b     2
c     2
d     1
b     4
c     1

I need to transform it into a NumPy array of 2D-arrays where each 2D-array corresponds to one of the letters. For example, if 'a' doesn't occur together with 1 and 2, and occurs with 3 and 4, 2D array corresponding to it should look like [0, 0, 1, 1] . So in this example I need:

[[0, 0, 1, 1], [0, 1, 0, 1], [0, 1, 0, 0], [1, 0, 0, 1]]

What is the best way to do this?

Answer 1

Here is one way crosstab

l = pd.crosstab(df.col_1,df.col_2).values.tolist()
Out[23]: [[0, 0, 1, 1], [0, 1, 0, 1], [1, 1, 0, 0], [1, 0, 0, 0]]