python - Convert two columns Pandas data frame to dictionary of list with first column as keys

Question

I have the following data frame:

import pandas as pd

df = pd.DataFrame({
    "ClusterID" : [1,2,2,1,3],
    "Genes" : ['foo','qux','bar','cux','fii'],
})

Which looks like this:

  ClusterID Genes
0          1   foo
1          2   qux
2          2   bar
3          1   cux
4          3   fii

What I want to do is to convert them into a dictionary of list:

{ '1': ['foo','cux'],
  '2': ['qux','bar'],
  '3': ['fii']}

How can I do that?

Answer 1

You can use groupby and apply tolist and then use Series.to_dict:

import pandas as pd

df = pd.DataFrame({
    "ClusterID" : [1,2,2,1,3],
    "Genes" : ['foo','qux','bar','cux','fii'],
})
print df
   ClusterID Genes
0          1   foo
1          2   qux
2          2   bar
3          1   cux
4          3   fii

s = df.groupby('ClusterID')['Genes'].apply(lambda x: x.tolist())
print s
ClusterID
1    [foo, cux]
2    [qux, bar]
3         [fii]
Name: Genes, dtype: object

print s.to_dict()
{1: ['foo', 'cux'], 2: ['qux', 'bar'], 3: ['fii']}