CODEWITHSUNDEEP
pythonpandas
Joe
Joe

Reputation: 889

Faster way to concatenate a column value to all values in another column pandas, do for all values in the first column

I'm looking for a faster way to concatenate a value of first column to all the values of the second column for all values in the first column.

This is achievable by looping through all values, yes, but my dataset is quite big and looping takes a while to finish.

Here's a replicated example:

import pandas as pd
df = pd.DataFrame({'col_1':['a','b','c'], 'col_2':['d','e','f']})
df
  col_1 col_2
0     a     d
1     b     e
2     c     f

I want a new dataframe that returns:

 col_1
0   a d
1   a e
2   a f
3   b d
4   b e
5   b f
6   c d
7   c e
8   c f

I can't quite phrase the right term to search for.

There might be a vetorized approach to achieve this or a pandas method. Answers or link to a similar question/s will be appreciated.

Thanks in advance :)

Upvotes: 2

Views: 238

Answers (2)

Erfan
Erfan

Reputation: 42926

Using DataFrame.merge:

df['key'] = 1
mrg = df[['col_1', 'key']].merge(df[['col_2', 'key']], on='key').drop(columns='key')

  col_1 col_2
0     a     d
1     a     e
2     a     f
3     b     d
4     b     e
5     b     f
6     c     d
7     c     e
8     c     f

Upvotes: 4

anky
anky

Reputation: 75120

Use itertools.product here:

import itertools
pd.DataFrame([' '.join(i) for i in itertools.product(df.col_1,df.col_2)],columns=['col1'])

  col1
0  a d
1  a e
2  a f
3  b d
4  b e
5  b f
6  c d
7  c e
8  c f

Upvotes: 2

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