[FIXED] Best way to matchup & merge 2 seperate dataframes in python by column/row values?

Issue

I have 2 dataframes outputted from my python script: dt1 & dt2

Each dataframe has 4 columns (colA, colB, colC, & colD) and each dataframe has a different length (dt1 always has more rows)

I want to create a 3rd dataframe dt3 that:

1. copies dt1
2. adds dt2[colD] value to the corresponding row IF dt1[colA] = dt2[colA] & dt1[colB] = dt2[colB] & dt1[colC] = dt2[colC], if the 3 columns don't match I want to load null

I've tried iterating through using a for loop with combined if else statements but can't seem to get the check piece right, please help!

Solution

Use merge from pandas

df1.merge(df2[["colA","colB","colC","colD"]],on=["colA","colB","colC"])

Updated as Op req.

df1.colD.fillna('---')

Answered By - Suraj S