removing square brackets in creating a new column pandas

I have a pandas df, something like this:

     col1              col2             
     ABC       [hello, hi, hey, hiya]

my task is to extract the first three words of col2 into a new column with a hyphen in between. Something like this:

     col1              col2                 col3    
     ABC       [hello, hi, hey, hiya]    hello-hi-hey

this seemed simple enough, but I am not able to remove the square brackets anyway I try in new column. Is this possible to do? Any help will be appreciated.

>Solution :

Assuming a Series of lists, slice and join:

df['col3'] = df['col2'].str[:3].agg('-'.join)

If you rather have string representations of lists:

import re
df['col3'] = ['-'.join(re.split(', ', s[1:-1])[:3]) for s in df['col2']]

output:

  col1                    col2          col3
0  ABC  [hello, hi, hey, hiya]  hello-hi-hey