I'm trying to reshape a data frame in a certain way.

This is the data frame I have,

I'd like to reshape the dataframe such that it looks like this:

How would I go about doing this? (without changing col_2 values)

CodePudding user response：

For expected ouput join both columns with removed matched values from col_1 by col_2:

df = pd.concat([df.col_2, df.loc[~df.col_1.isin(df.col_2), 'col_1']]).to_frame('col_3')
print (df)
     col_3
0  Roxanne
1    Ghina
2    Leila
3   George
4     Rock
5     Rock
0      One
1      Two
4    Three
5     Four

CodePudding user response：

You can use:

out = (df[['col_2', 'col_1']].melt(value_name='col_3')[['col_3']]
       .drop_duplicates(ignore_index=True)
      )

Or:

out = (df.loc[:, ::-1].unstack().reset_index(drop=True).to_frame(name='col_3')
       .drop_duplicates(ignore_index=True)
      )

output:

     col_3
0  Roxanne
1    Ghina
2    Leila
3   George
4     Rock
5      One
6      Two
7    Three
8     Four