How do I expand my pands dataframe through a loop?

Question

So I have a table like this in my pandas dataframe

#	A	B
0	f	1
1	g	2

But idk what code to write to transform it to

#	A	B
0	f	1a
1	f	1b
2	g	2a
3	g	2b

Asked By: van dam

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Source

Answer 1

Assuming you want a cross product:

import numpy as np
import pandas as pd

df = pd.DataFrame({'#': [0, 1], 'A': list('fg'), 'B': [1, 2]})

l = ['a', 'b']

out = (
 df.loc[df.index.repeat(len(l))]
   .assign(**{'B': lambda d: d['B'].astype(str)+np.tile(l, len(df)),
              '#': lambda d: range(len(d))})
 )

Or with a cross merge:

out = (
 df.merge(pd.Series(l, name='tmp'), how='cross')
   .assign(**{'B': lambda d: d['B'].astype(str)+d.pop('tmp'),
              '#': lambda d: range(len(d))})
)

Output:


   #  A   B
0  0  f  1a
0  1  f  1b
1  2  g  2a
1  3  g  2b

Answered By: mozway

How do I expand my pands dataframe through a loop?

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