Pandas – select column using other column value as column name

by

You can use lookup:

df['new_col'] = df.lookup(df.index, df.names)
df
#   a    b  names   new_col
#0  1   -1      a   1
#1  2   -2      b   -2
#2  3   -3      a   3
#3  4   -4      b   -4

EDIT

lookup has been deprecated, here’s the currently recommended solution:

idx, cols = pd.factorize(df['names'])
df.reindex(cols, axis=1).to_numpy()[np.arange(len(df)), idx]

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