Pandas column values to columns?

Question

I've seen a few variations on the theme of exploding a column/series into multiple columns of a Pandas dataframe, but I've been trying to do something and not really succeeding with the existing approaches.

Given a DataFrame like so:

    key       val

id

2   foo   oranges

2   bar   bananas

2   baz   apples

3   foo   grapes

3   bar     kiwis

I want to convert the items in the key series into columns, with the val values serving as the values, like so:

 

        foo        bar baz

id

2   oranges    bananas apples

3    grapes      kiwis NaN

I feel like this is something that should be relatively straightforward, but I've been bashing my head against this for a few hours now with increasing levels of convolution, and no success.

Answer 1

You can simply use set_index and unstack

In [1923]: df.set_index([df.index, 'key'])['val'].unstack()

Out[1923]:

key      bar baz      foo

id

2    bananas  apples oranges

3      kiwis   None grapes

Or, a simplified groupby:

In [1926]: df.groupby([df.index, 'key'])['val'].first().unstack()

Out[1926]:

key      bar baz      foo

id

2    bananas  apples oranges

3      kiwis   None grapes

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