Creating a new column in pandas dataframe as a function of another column

Question

My pandas dataframe has an existing column, "div", which has a string. I want to make a new column ('newcol') whose value equals the first character of the string in div.

I've tried to specify this several ways but it doesn't work.

results['newcol'] = results['div'] gives me the full string (as expected) not the first char.

results['newcol'] = results['Div'].values[0] and results['newcol'] = results['Div'][0] makes the newcol in every row equal to the 'Div' string of the first row.

results['newcol'] = str(results['Div']) and results['newcol'] = str(results['Div'])[0] convert the entire ['Div']series into a single string and returns that to newcol.

What's the correct way to specify what I want?

cel · Accepted Answer · 2014-12-26 12:44:06Z

7

This should work:

import pandas as pd
data = pd.DataFrame({"A": ["hello", "world"], "B": [1, 2]})
data["C"] = data.A.str[0]
data

This is the output:

  |   A   | B | C 
------------------
0 | hello | 1 | h
------------------
1 | world | 2 | w

answered Dec 26, 2014 at 12:44

cel

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