How can I use values from a Pandas data frame in a calcul?

June 3, 2022

I have a Pandas data frame. In the A columns there are ints like [1, 5, 3], and in the B columns there are string like ["abcdef", "ghijklmno", "qwertyuiop"]

I want to create a C columns with the columns B first char according to the culumns A. In my example I want the C columns to be like ["a", "ghijk", "qwe" ]

I tried:

data_frame['C'] = data_frame.B.str[:data_frame["A"]]

But it doesn’t work.

>Solution :

You can set use a lambda function and set the axis = 1 to use column A to set the string length of B

df = pd.DataFrame({
    'A' : [1, 5, 3,],
    'B' : ["abcdef", "ghijklmno", "qwertyuiop"]
})
df['c'] = df.apply(lambda x : x['B'][:x['A']], axis = 1)
df