Replace a string in a column for each row of a pandas dataframe

Question

Edit: I had to add this part to my original question as it's relevant.

I have a frame which contains many different prefixes in the name column called dfload.

I use the following command to create a slice called df.

df = dfload.loc[dfload['Name'].str.contains("testData/")]

Original Question continues from here:

Then, I have the following pandas dataframe called df,

   name               etc etc etc
0  testData/example1  etc ...
1  testData/example2  ...
2  testData/example3
3  testData/example4
...

I want to replace the string testData/ with nothing for the entire column so it looks like this

   name      etc etc etc
0  example1  etc ...
1  example2  ...
2  example3
3  example4
...

I used the following command df['name'] = df['name'].str.replace('testData/','').

But I get this error,

<ipython-input-20-dae746394d2d>:1: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  df['name'] = df['name'].str.replace('testData/','')

The dataframe looks fine, why am I getting this error? What's the "proper" way to do this?

you shouldn't, but you might be able to suppress the warning with df.loc[:,['name']] = df.name.str.replace('testdata/','') — EMiller
– EMiller, Commented Jun 24, 2020 at 22:56
ok I think it's happening because I made this frame from a slice of another frame, is that why? I used this command df = dfload.loc[dfload['Name'].str.contains("testData/")] — anarchy
– anarchy, Commented Jun 24, 2020 at 23:00

EMiller · Accepted Answer · 2020-06-24 23:20:17Z

2

to avoid the warning that you're getting, create df like this:

import pandas as pd
df = pd.DataFrame(dfload[dfload.name.str.contains('testdata/')])

specifying that it's a dataframe and not a slice is probably what keeps pandas from throwing the warning

answered Jun 24, 2020 at 23:20

EMiller

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2 Comments

anarchy Over a year ago

I've never made slices that way, it works!. learned something new thanks

EMiller Over a year ago

@anarchy I think that the majority of the work was actually figuring out how to reproduce the warning. Thank you for showing me the precise origin of a warning that pandas has given me many times.

Oladimeji Mudele · Accepted Answer · 2020-06-24 22:44:58Z

0

Use this:

df.name = df.name.str.replace('testData/','',regex = True)

answered Jun 24, 2020 at 22:44

Oladimeji Mudele

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2 Comments

Oladimeji Mudele Over a year ago

It is a warning btw, and not an error. Is this your whole code?

anarchy Over a year ago

I updated my question, I think its the previous command I used that's causing this. could you take a look

Daniela Varela · Accepted Answer · 2020-06-24 22:48:48Z

0

You should try using lamda funtion to apply the replace statement over every row:

df["name"]= df.apply(lambda x: x['name'].replace('testData/',''), axis=1)

answered Jun 24, 2020 at 22:48

Daniela Varela

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