Print column headers of datafreame in Python using Pandas

Question

I have an input data frame which looks like this:

print (df)
    Id  A  B  C  D
0  101  0  0  0  1
1  102  0  0  0  0
2  103  1  0  1  0
3  104  1  0  1  1

Output: I want to print the Column Names of the columns which contain '1' in it. The output data frame should look like this. If 1 is not present it should return an empty string.

Id 101- D (4th index) has 1
Id 102- None
Id 104- A, C and D which are 1,3,4 indexes

So, a sample output would look like:

print (df)
    Id  Result
0  101       D
1  102        
2  103     A,C
3  104   A,C,D

I have tried this code but it didn't work:


df['out'] = df.apply(
    lambda x: ','.join(str(ele) for ele in [df.column for df.column,df.column.values in enumerate(x[:]) if df.column.values is 1]), 
    axis=1)

df_out

jezrael · Accepted Answer · 2021-05-17 06:26:44Z

3

Use DataFrame.dot with all columns without first for matrix multiplication, add separator and last remove last character (separator) by indexing:

df['Result'] = df.iloc[:, 1:].dot(df.columns[1:] + ',').str[:-1]
print (df)
    Id  A  B  C  D Result
0  101  0  0  0  1      D
1  102  0  0  0  0       
2  103  1  0  1  0    A,C
3  104  1  0  1  1  A,C,D

Your solution should be changed with extract matched index with join:

df['Result'] = df.apply(lambda x: ','.join(x.index[1:][x.iloc[1:] == 1]), axis=1)
print (df)
    Id  A  B  C  D Result
0  101  0  0  0  1      D
1  102  0  0  0  0       
2  103  1  0  1  0    A,C
3  104  1  0  1  1  A,C,D

answered May 17, 2021 at 6:26

jezrael

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