Creating New Column In Pandas Dataframe Using Regex [duplicate]

Question

I have a column in a pandas df of type object that I want to parse to get the first number in the string, and create a new column containing that number as an int.

For example:

Existing df

    col
    'foo 12 bar 8'
    'bar 3 foo'
    'bar 32bar 98'

Desired df

    col               col1
    'foo 12 bar 8'    12
    'bar 3 foo'       3
    'bar 32bar 98'    32

I have code that works on any individual cell in the column series

int(re.search(r'\d+', df.iloc[0]['col']).group())

The above code works fine and returns 12 as it should. But when I try to create a new column using the whole series:

df['col1'] = int(re.search(r'\d+', df['col']).group())

I get the following Error:

TypeError: expected string or bytes-like object

I tried wrapping a str() around df['col'] which got rid of the error but yielded all 0's in col1

I've also tried converting col to a list of strings and iterating through the list, which only yields the same error. Does anyone know what I'm doing wrong? Help would be much appreciated.

check out the DataFrame.apply() method. Probably your computation is too complex for a simple assign. — Dave Kielpinski
– Dave Kielpinski, Commented Sep 21, 2017 at 18:18

Albo · Accepted Answer · 2023-01-11 07:07:17Z

17

This will do the trick:

new_column = []    
for values in df['col']:
    new_column.append(re.search(r'\d+', values).group())

df['col1'] = new_column

the output looks like this:

            col    col1
0  foo 12 bar 8      12
1     bar 3 foo       3
2  bar 32bar 98      32

edited Jan 11, 2023 at 7:07

answered Sep 21, 2017 at 18:41

Albo

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2 Comments

RolfBly Over a year ago

The list has the same name as the regex method (search), which I find a bit confusing. mylist = [], mylist.append... would imho make it a clearer example.

Sergo055 Over a year ago

stackoverflow.com/questions/58973981/… this approach is much better. Using a for loop in a dataframe is an instant red flag

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