convert a pandas dataframe to dictionary

Question

I have a pandas dataframe as below:

df=pd.DataFrame({'a':['red','yellow','blue'], 'b':[0,0,1], 'c':[0,1,0], 'd':[1,0,0]})
df

which looks like

    a       b   c   d
0   red     0   0   1
1   yellow  0   1   0
2   blue    1   0   0

I want to convert it to a dictionary so that I get:

red     d
yellow  c
blue    b

The dataset if quite large, so please avoid any iterative method. I haven't figured out a solution yet. Any help is appreciated.

Answer 1

First of all, if you really want to convert this to a dictionary, it's a little nicer to convert the value you want as a key into the index of the DataFrame:

df.set_index('a', inplace=True)

This looks like:

        b  c  d
a              
red     0  0  1
yellow  0  1  0
blue    1  0  0

Your data appears to be in "one-hot" encoding. You first have to reverse that, using the method detailed here:

series = df.idxmax(axis=1)

This looks like:

a
red       d
yellow    c
blue      b
dtype: object

Almost there! Now and use to_dict on the 'value' column (this is where setting column a as the index helps out):

series.to_dict()

This looks like:

{'blue': 'b', 'red': 'd', 'yellow': 'c'}

Which I think is what you are looking for. As a one-liner:

df.set_index('a').idxmax(axis=1).to_dict()

Answer 2

You can try this.

df = df.set_index('a')
df.where(df > 0).stack().reset_index().drop(0, axis=1)


    a   level_1
0   red     d
1   yellow  c
2   blue    b