Pandas replace cell value for matching index between two dataframes

Question

I have a large DataFrame and I want to change the column value 'Final_Status' for the matching fields:

#df_full:
EMG Final_Status
G05AT   Fail
G05AZ   Fail
O05AP   Pass
O05AZ   Fail
O15AP   Fail
O51AK   Fail
T05AP   Fail

#df_overwrite:
EMG Final_Status
G05AT   Pass
G05AZ   Pass

#final result:
#df_full:
EMG Final_Status
G05AT   Pass
G05AZ   Pass
O05AP   Pass
O05AZ   Fail
O15AP   Fail
O51AK   Fail
T05AP   Fail

I can do it by looping over all rows of the smaller df (df_overwrite) but loops make my code very slow. Is there another way?

ALollz · Accepted Answer · 2020-08-17 15:52:55Z

2

Take advantage of the Index in pandas to force alignment, then you want update. You can .reset_index() if you want 'EMG' back as a column.

df_full = df_full.set_index('EMG')
df_overwrite = df_overwrite.set_index('EMG')

df_full.update(df_overwrite, overwrite=True)
print(df_full)

      Final_Status
EMG               
G05AT         Pass
G05AZ         Pass
O05AP         Pass
O05AZ         Fail
O15AP         Fail
O51AK         Fail
T05AP         Fail

answered Aug 17, 2020 at 15:52

ALollz

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Comments

Tom · Accepted Answer · 2020-08-17 16:00:39Z

0

You can also use loc here (assuming EMG is the index):

df_full.loc[df_overwrite.index] = df_overwrite

answered Aug 17, 2020 at 16:00

Tom

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1 Comment

Adnan Hadi Over a year ago

yes this also works, i had to modify a bit as i had more columns in df_full df_full.loc[df_ow.index,'Final_Status'] = df_ow['Final_Status']

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