"Length of values does not match length of index" when extracting substring in dataframe

Question

I am trying to extract daynumber from datetime column in a new column, like so

df_merged['tr_date'] = df_merged['tr_datetime'].str.split(' ')[0]

When I run this code, I get the following error

Length of values does not match length of index

Here is a sample of the df_merged data

Answer 1

Use:

df_merged['tr_date'] = df_merged['tr_datetime'].apply(lambda x: x.split(' ')[0])