I have a pandas dataframe 'df' with two columns 'A' and 'B', I have a function with two arguments
def myfunction(B, A):
# do something here to get the result
return result
and I would like to apply it row-by-row to df using the 'apply' function
df['C'] = df['B'].apply(myfunction, args=(df['A'],))
but I get the error
ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().
whats happening here, it seems it takes df['A'] as the whole series. not just the row entry from that series as required.
I think you need:
import pandas as pd
df = pd.DataFrame({'A':[1,2,3],
'B':[4,5,6]})
print (df)
A B
0 1 4
1 2 5
2 3 6
def myfunction(B, A):
#some staff
result = B + A
# do something here to get the result
return result
df['C'] = df.apply(lambda x: myfunction(x.B, x.A), axis=1)
print (df)
A B C
0 1 4 5
1 2 5 7
2 3 6 9
Or:
def myfunction(x):
result = x.B + x.A
# do something here to get the result
return result
df['C'] = df.apply(myfunction, axis=1)
print (df)
A B C
0 1 4 5
1 2 5 7
2 3 6 9
I would add one more method, which could be useful when you need pass all columns to the function.
We consider that according to pandas.DataFrame.apply
docs: Objects passed to the function are Series objects . So we convert pd.Series
to list
. Then unpack it using *
operator, while our function call.
import pandas as pd
df = pd.DataFrame({'A':[1,2,3],
'B':[4,5,6]})
print (df)
A B
0 1 4
1 2 5
2 3 6
def myfunction(B, A):
#some staff
result = B + A
# do something here to get the result
return result
df['C'] = df.apply(lambda x: myfunction(*x.to_list()), axis=1)
print (df)
A B C
0 1 4 5
1 2 5 7
2 3 6 9
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