update column in on data frame with value of column from another data frame

New comment
 

Hi there

In Python 3.7 , I need some help with the syntax of updating data frame with value from another data frame:

I have a trade and it has 2 rows - one for the start and one for the end

I would like to update the start time in end row.

for example - df_start (start trades) and df_end (end trades) - the column position_id is identical between the tow (this column is the key for the 2 data frames) 

I need the column time in  df_end to change like that :  df_end['time'] = df_start['time']


Thanks for the help :)

New comment