Overwrite columns in DataFrames of different sizes pandas

Question

I have following two Data Frames:

df1 = pd.DataFrame({\'ids\':[1,2,3,4,5],\'cost\':[0,0,1,1,0]})
df2 = pd.DataFrame({\'ids\':[1,5],\'cost\':[1,4]})
         


        

Answer 1

Another way to do it, using a temporary merged dataframe which you can discard after use.

import pandas as pd

df1 = pd.DataFrame({'ids':[1,2,3,4,5],'cost':[0,0,1,1,0]})
df2 = pd.DataFrame({'ids':[1,5],'cost':[1,4]})

dftemp = df1.merge(df2,on='ids',how='left', suffixes=('','_r'))
print(dftemp)

df1.loc[~pd.isnull(dftemp.cost_r), 'cost'] = dftemp.loc[~pd.isnull(dftemp.cost_r), 'cost_r']
del dftemp 

df1 = df1[['ids','cost']]
print(df1)


OUTPUT-----:
dftemp:
   cost  ids  cost_r
0     0    1     1.0
1     0    2     NaN
2     1    3     NaN
3     1    4     NaN
4     0    5     4.0

df1:
   ids  cost
0    1   1.0
1    2   0.0
2    3   1.0
3    4   1.0
4    5   4.0