Change row values in specific pandas data frame column with python

Question

Following problem.

I have a data frame with the following format.

   Col1 Col2 Col3 Col4  
1    0    0    0    0
2    0    0    0    0

Furthermore, I have a List of values that match the column names:

ColNameList1 = [Col1, Col3] #list for the first row
ColNameList2 = [Col3, Col4] #list for the second row

The target is to change the value of 0 to 1 for every column row match.

    Col1 Col2 Col3 Col4  
1    1    0    1    0 
2    0    0    1    1

I did some intense research on the Pandas documentation and also google and stack overflow but it seems there is not a fitting solution for this problem.

As always any help is much appreciated.

Allen Qin · Accepted Answer · 2017-07-03 04:39:45Z

20

You can simply use loc and set values:

df.loc[1,ColNameList1]=1

df.loc[2,ColNameList2]=1

df
Out[10]: 
   Col1  Col2  Col3  Col4
1     1     0     1     0
2     0     0     1     1

answered Jul 3, 2017 at 4:39

Allen Qin

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5 Comments

Saibottrenham Over a year ago

thanks for the prompt reply, I got the error AttributeError: 'int' object has no attribute 'loc'. Do I miss something?

Allen Qin Over a year ago

That's strange. Is your df actually a pandas dataframe? Can you show the complete error stack trace?. Can you also do a df.head()?

jarry jafery Over a year ago

you should check the data type of your data frame it seems to be some problem.

Saibottrenham Over a year ago

pandas version 0.19.2

df = pd.DataFrame() df['Col1'] = [0, 0] df['Col2'] = [0, 0] df['Col3'] = [0, 0] df['Col4'] = [0, 0]  print df  print type(df) ColNameList1 = ['Col1', 'Col3'] #list for the first row ColNameList2 = ['Col3', 'Col4'] #list for the second row df = df.loc[1,ColNameList2]=1  print df

when I run this code i get ` Col1 Col2 Col3 Col4 0 0 0 0 0 1 0 0 0 0 <class 'pandas.core.frame.DataFrame'> AttributeError: 'int' object has no attribute 'loc' `

Allen Qin Over a year ago

2 problems: a:) You can't do df = df.loc[1,ColNameList2]=1, just do df.loc[1,ColNameList2]=1. b:) In your example data, the df index is 1 based here it appears to be 0 based. If it's 0 based, you need to use df.loc[0] and df.loc[1] respectively.

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