Left Join In Pandas Without The Creation Of Left And Right Variables

I'm missing something in the syntax of merging in pandas. I have the following 2 data frames: >>> dfA s_name geo zip date value 0 A002X zip 60601 2010 None 1

Solution 1:

I think you need combine_first with MultiIndex created by set_index:

cols = ["s_name","geo","zip","date"]

df = dfA.set_index(cols).combine_first(dfB.set_index(cols)).reset_index()
print (df)
  s_name  geo    zip  date  value
0  A002X  zip  60601  2010    1.0
1  A002Y  zip  60601  2010    2.0
2  A003X  zip  60601  2010    NaN
3  A003Y  zip  60601  2010    4.0

Or update:

df = dfA.set_index(cols)
df.update(dfB.set_index(cols))
df = df.reset_index()