Go through cells of a single column, and apply a formula to them if they meet a certain condition using Pandas?

Question

Doing some data cleaning in a CSV file. I want to convert some CSV data into HTML before uploading the data to a website.

I'm going through every cell in the column called 'Details' in a pandas dataframe.

If a cell starts with this character combination: \r\r\n \t , then I want to replace it with this: <ul><li>

 df2 = df.copy() def startswith_replace (x, a, b): if x.startswith(a): x.replace(a, b) df2['Details'] = df2['Details']. apply(lambda x: startswith_replace(x, '\\r\\r\\n \\t', '\<ul\>\<li\>'))

When I run this, however, every cell in the 'Details' column is replaced with 'None' as its value.

Answer 1

This can be accomplished using the built-in Series.str.replace without needing to define your own function, with just a little regex

( ^ to only check the start of the string and () optionally to set it as a capture group, but if you decide you want to replace all occurrences both can be omitted and the raw string passed)

df

    A   B   A   Details
0   1   2   3   \r\r\n \t
1   4   5   6   lkjn \r\r\n \t
2   7   8   9   abcdefg

df['Details']=df['Details'].str.replace(r'^(\r\r\n \t)','\<ul\>\<li\>')

    A   B   A   Details
0   1   2   3   \<ul\>\<li\>
1   4   5   6   lkjn \r\r\n \t
2   7   8   9   abcdefg