List comprehension not working as intended

November 30, 2021

Let’s say my dataframe is like this:

Used the following code to split data inside each column:

    col_names = ['col1','col2','col3']
    for i in range(len(df)):
        s = tuple(zip(df[col_names[0]].str.split(",")[i],df[col_names[1]].str.split(",")[i],df[col_names[2]].str.split(",")[i])

I changed this code so that it works dynamically to work for a variable number of columns in col_names using list comprehension as seen below:

for i in range (len(df)):
    s = tuple(zip(df[col].str.split(",")[i] for col in col_names)

Initial code used to give output as:

But now after adding list comprehension it looks like:

what is wrong in this code?

>Solution :

#1) Your code is extremely inefficient since its calling df[col].str.split(",") over and over again for every i.

#2) Your immediate bug is the zip. You are passing it a single iterator as an argument. You need to pass it multiple arguments. The correct way to convert is zip(*(........))