How do you append the values of the first column to all other columns in a pandas dataframe

Question

I have been trying to search on how to get the value of the first column and append it to the remaining columns in the dataframe but the ones that I have seen need to still make a new column for the new output.

The closest that I found based on what I need is this code.

df['col'] = 'str' + df['col'].astype(str)

Below is a sample of my dataframe

      col1        col2    col3    col4
1  02-04-2017      ND     0.32     0.8
2  02-05-2017      0.3     ND     No Connection

What I want to know is, how can I get this output?

      col1         col2               c ol3                col4
1  02-04-2017   ND|02-04-2017     0.32|02-04-2017      0.8|02-04-2017 
2  02-05-2017   0.3|02-05-2017    ND|02-05-2017        No Connection|02-05-2017

Answer 1

You can do this a little easily with df.iloc and str.cat:

df.iloc[:, 1:] = df.iloc[:, 1:].apply(lambda x: x.str.cat(df['col1'], sep='|'))   
df

         col1            col2             col3                      col4
1  02-04-2017   ND|02-04-2017  0.32|02-04-2017            0.8|02-04-2017
2  02-05-2017  0.3|02-05-2017    ND|02-05-2017  No Connection|02-05-2017

---

You could also use df.transform (v0.20 onwards).

df.iloc[:, 1:] = df.iloc[:, 1:].transform(lambda x: x.str.cat(df['col1'], sep='|'))   
df

         col1            col2             col3                      col4
1  02-04-2017   ND|02-04-2017  0.32|02-04-2017            0.8|02-04-2017
2  02-05-2017  0.3|02-05-2017    ND|02-05-2017  No Connection|02-05-2017

Answer 2

Fun with assign, add, and radd

df.assign(**df.iloc[:, 1:].astype(str).add(df.col1.radd('|'), 0))

         col1            col2             col3                      col4
1  02-04-2017   ND|02-04-2017  0.32|02-04-2017            0.8|02-04-2017
2  02-05-2017  0.3|02-05-2017    ND|02-05-2017  No Connection|02-05-2017