Selecting single values from pandas dataframe using lists

Question

import numpy as np
import pandas as pd

ind = [0, 1, 2]
cols = ['A','B','C']
df = pd.DataFrame(np.arange(9).reshape((3,3)),columns=cols)

Say you have a pandas dataframe df looking like:

    A  B  C
 0  0  1  2
 1  3  4  5
 2  6  7  8    

If you want to capture a single element from each column in cols at a specific index ind the output should look like a series:

 A  0
 B  4
 C  8

What I've tried so far was:

 df.loc[ind,cols]

which gives the undesired output:

   A  B  C
0  0  1  2
1  3  4  5
2  6  7  8

Any suggestions?

context: The next step would be mapping the output of an df.idxmax() call of one dataframe onto another dataframe with the same column names and indexes, but I can likely figure that out if I know how to do the above mentioned transformation .

Answer 1

you can use DataFrame.lookup():

In [6]: pd.Series(df.lookup(df.index, df.columns), index=df.columns)
Out[6]:
A    0
B    4
C    8
dtype: int32

or:

In [14]: pd.Series(df.lookup(ind, cols), index=df.columns)
Out[14]:
A    0
B    4
C    8
dtype: int32

Explanation:

In [12]: df.lookup(df.index, df.columns)
Out[12]: array([0, 4, 8])