How to replace all instances of /N with NaN in a csv file using Python

Question

I've read a csv file into Python, and it contains many objects for which the value is \N. I need to replace all of those instances with 'NaN'.

I've gotten the file to read in correctly, but I get an error when I try to replace the \Ns.

import pandas as pd

df = pd.read_csv(r'file.csv')

df.replace('\N', 'NaN')

File "<ipython-input-63-a631ab1f5217>", line 3
    df.replace('\N', 'NaN')
              ^
SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 0-1: malformed \N character escape

is that a typo or do you have a r before the path to your csv-file? Also maybe use np.nan instead of 'NaN' — Quastiat
– Quastiat, Commented Oct 10, 2019 at 21:42
pandas read_csv accepts a parameter called na_values which can be used to set any string as NaN directly when reading the file. You could do: df = pd.read_csv(r'file.csv', na_values='\N') (or \\N again) and drop the df.replace call. — Valentino
– Valentino, Commented Oct 10, 2019 at 21:47

3NiGMa · Accepted Answer · 2019-10-10 22:31:22Z

1

Python uses backslashes as a symbol to signify escape sequences like newlines, tabs, quotes, etc. So if you want to use backslashes in a string, you must replace all the single backslashes with double backslashes, like so;

df.replace('\\N', 'NaN')

answered Oct 10, 2019 at 22:31

3NiGMa

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leftjoin · Accepted Answer · 2022-01-14 14:22:27Z

0

Pass na_values="\\N" parameter:

df = pd.read_csv('file.csv',na_values="\\N")

Double backslash should be used to escape backslash.

answered Jan 14, 2022 at 14:22

leftjoin

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