Set value of a column based on values of other columns (Pandas)

Question

The last time I used Python is some time ago so some things have faded away.

I have a given dataset, with multiple columns. I want to create a new column and set the values based on multiple values (text or value) of other columns.

So in the example below, c1 consists of [a,a,b,b] and c2 of [a,b,a,b]. Now I want the new column c3 to be [1,2,3,4]

All help is appreciated!

import pandas as pd
data = pd.read_excel('data')

data['c3'] = 0

for i in range(len(data.c3)):
    if data.c1[i] == a and data.c2[i] == a:
        data.c3[i] == 1
    elif data.c1[i] == a and data.c2[i] != a:
        data.c3[i] == 2
    elif data.c1[i] != a and data.c2[i] == a:
        data.c3[i] == 3
    elif data.c1[i] != a and data.c2[i] != a:
        data.c3[i] == 4```

Answer 1

I would use apply. It allows you to perform a function row-wise or column-wise. Check this post on StackOverflow, it provides good examples of what this looks like.

The gist is:

• create a function that creates the value you want based on a row
• use apply to create a dataframe containing the results
• if you're happy with the results, merge that dataframe into your existing one