Pandas: Search for dataframe row by string then modify [without header]

Question

A bit of pickle. I am trying to find a single row in a dataframe by searching for a specific string value, then replace the string value with zero. I am using the following code:

selectRow = df[df.iloc[:,0].str.match(ID)]

selectRow.replace(ID, 0)

where ID is some string. This returns one row within the dataframe as expected. However, I can't seem to modify the values of the selectRow in dataframe, as the selectRow is a separate dataframe at this point.

I know I am missing something incredibly basic. Any help would be much appreciated!

CN

P.S. dataframe I am working on is without header, and I would prefer to keep it that way - ideally. — CockneyNinja
– CockneyNinja, Commented Oct 14, 2019 at 18:08
you can just assign it in your first call provided you know which column it is you want to change based on index — gold_cy
– gold_cy, Commented Oct 14, 2019 at 18:10
after replace, try update selectRow back to df as: df.update(selectRow) — Andy L.
– Andy L., Commented Oct 14, 2019 at 18:14
Sorry, could you elaborate on "assigning it to the first call"? I've tried df.update but it didn't make any changes. :( — CockneyNinja
– CockneyNinja, Commented Oct 14, 2019 at 18:16

CypherX · Accepted Answer · 2019-10-14 19:09:01Z

1

You could do it in a single line as follows:

Method-1:

ID = `eee`
df.iloc[:,0].loc[df.iloc[:,0]==ID] = 0

Output:

        C1   C2
0      aaa  bbb
1      ccc  ddd
2        0  fff
3  ggg eee  hhh

Method-2:

Use pandas.Dataframe.replace method.

df.iloc[:,0].replace(to_replace=ID, value=0, regex=False)

Output:

        C1   C2
0      aaa  bbb
1      ccc  ddd
2        0  fff
3  ggg eee  hhh

If you set regex=True, that could adjust the rows based on other occurrences of the ID as well. Output:

        C1   C2
0      aaa  bbb
1      ccc  ddd
2        0  fff
3        0  hhh

Dummy Data

df = pd.DataFrame([['aaa','bbb'],['ccc','ddd'],['eee','fff'],['ggg eee','hhh']], columns=['C1','C2'])
print(df)

Output:

        C1   C2
0      aaa  bbb
1      ccc  ddd
2      eee  fff
3  ggg eee  hhh

edited Oct 14, 2019 at 19:09

answered Oct 14, 2019 at 18:50

CypherX

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Comments

Alexey · Accepted Answer · 2019-10-14 18:41:06Z

0

test data:

import pandas as pd
df = pd.DataFrame([['aaa','bbb'],['ccc','ddd'],['eee','fff'],['ggg','hhh']])

df is:

    Out[42]: 
         0    1
    0  aaa  bbb
    1  ccc  ddd
    2  eee   fff
    3  ggg  hhh

code:

Template = 'eee'
df[0] = [(lambda x: 0 if (x == Template) else x)(x) for x in df[0]]

Result is:

Out[45]: 
         0    1
    0  aaa  bbb
    1  ccc  ddd
    2    0  fff
    3  ggg  hhh

Does it help?

edited Oct 14, 2019 at 18:41

answered Oct 14, 2019 at 18:34

Alexey

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Pandas: Search for dataframe row by string then modify [without header]

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