too many values to unpack in apply function (python 2)

Question

i wrote a simple function to split a string.

def split2(target):
   (key, host) = target.split('_')
   return (key, host)

(combined['host'], combined['timestamp']) = combined['key'].apply(split2)

combined['key'] is a pandas series that make of string like 'ibmserver_4/12/2007'

after trying multiple times, i still have the ValueError: too many values to unpack. if i reduce the return parameter in the split2 function to one, that works fine.

Can someone advise what's wrong with the code above and how should I rectify? Many thanks.

Answer 1

A simpler way would be to split the str directly with pandas, using expand=True creates separate columns, e.g.:

>>> combined['key'].str.split('_', expand=True)
           0          1
0  ibmserver  4/12/2007

The correct way to assign that to multiple columns is:

>>> combined[['host', 'timestamp']] = combined['key'].str.split('_', expand=True)
>>> combined
                   key       host  timestamp
0  ibmserver_4/12/2007  ibmserver  4/12/2007

To make your function work you would need to convert the returned tuple into a series, e.g.:

>>> combined[['host', 'timestamp']] = combined['key'].apply(split2).apply(pd.Series)