how to compare two columns in dataframe and update a column based on matching fields-CodePudding

I have two dataframe as shown below

|a|b|c|
|1|2| |
|4|5| |
|7|8| |

2nd dataframe is

|a_1|b_1|
|1  |5  |
|4  |2  |
|7  |8  |

I want to compare two common columns (a,a_1) and update the 3rd column in my 1st dataframe. Expected output is shown below

    |a|b|c|
    |1|2|5|
    |4|5|2|
    |7|8|8|

Is there a code to match common column and populate 3rd column?

CodePudding user response：

import pandas as pd

d1={
    "a":(1,4,7),
    "b":(2,5,8),
    "c":(0,0,0)
}

d2={
    "a_1": (1, 4, 7),
    "b_1": (5, 2, 8)
}

df1=pd.DataFrame(d1)
df2=pd.DataFrame(d2)

# Iterate through each entry in a and compare it to a_1
for i in range(len(df1["a"])):
    for j in range(len(df2["a_1"])):
        if df1["a"][i] == df2["a_1"][j]:
            df1["c"][i] = df2["b_1"][j]