从不同列的唯一值编制索引

Question

I have a dataframe with a bunch of columns and rows, and I want to get the data in one column based on the unique values in another column.

  flag  name
0  1     bob
1  2     larry
2  1     alice
3  1     mary
4  3     peter
5  4     rick

if a use

df['flag'].unique()

I get 1 2 3 4

How do I get the names that correspond to those unique values?

ie

  flag  name
0  1     bob
1  2     larry
4  3     peter
5  4     rick

It doesn't matter if I get bob, alice, or mary. I just need a name for that flag value.

Answer 1

By using drop_duplicates

df.drop_duplicates(['flag'])
Out[1036]: 
   flag   name
0     1    bob
1     2  larry
4     3  peter
5     4   rick

Answer 2

Wen's answer is simpler, but another way is to use groupby() and then take the first entry per group using nth() :

import pandas as pd

df = pd.DataFrame({'flag':[1, 2, 1, 1, 3, 4],
                   'name':['bob', 'larry', 'alice', 'mary', 'peter', 'rick']})

print df.groupby('flag').nth(0)

Result:

       name
flag       
1       bob
2     larry
3     peter
4      rick