Python loop multiple positional arguments to function from dataframe or array

Question

I have .csv file with colums A and B, and rows with values.

A,	B
232.65,	-57.48
22.69,	-5.46
23.67,	-7.71

I want to loop these values with function.

So lets create simple function with 2 positional parameters:

def add_numbers(n1, n2):
    answer = n1+n2
    print(answer)

#lets read the file:
import pandas as pd
df= pd.read_csv(r'myfile.csv')

print(df[A]) #just checking the column A for this example, but column B is also required for n2.
0   232.65
1   22.69
3   23.67

I could also transfer those colums to array but I still could not loop it. How would I loop these with the function that requires two arguments?


arr = np.loadtxt(r'myfile.csv', delimiter=',')
arr

array([[232.65, -57.48],
       [22.69, -5.46],
       [23.67, -7.71],

I have been trying to loop with various ways and iter and enumerate and apply, but I keep doing something slightly wrong.

Cheer, Joonatan

Check out https://stackoverflow.com/a/16476974/2794417 on how to loop throughj dataframe. Check out: https://stackoverflow.com/a/37428259/2794417 on how to apply a function to all rows of dataframe. — Galo do Leste, Feb 13 '23 at 03:52
Does this answer your question? [How to iterate over rows in a DataFrame in Pandas](https://stackoverflow.com/questions/16476924/how-to-iterate-over-rows-in-a-dataframe-in-pandas) — J_H, Feb 13 '23 at 03:54
I did read those before. My issue was that I basically know how to iterate, but not with a function. I can do it with list when only 1 positional argument is required. But not with df when there are two positional arguments required. Well I will have to continue then reading tomorrow. It is just that those samples were "how to edit" dataframe with iterating, for example adding colums. That I can do. Or how to loop list with SINGLE positional argmunt. I have now searched 14 hours answer for this, so I need to continue tomorrow. — Joonatan, Feb 13 '23 at 04:09

score 1 · Accepted Answer · answered Feb 13 '23 at 04:28

1

You can loop and pass the values in each row to add_numbers. Then use iterrows to get the index and row values.

def add_numbers(n1, n2):
answer = n1 + n2
print(answer)
    
import pandas as pd
df = pd.read_csv(r'myfile.csv')
    
for index, row in df.iterrows():
    add_numbers(row['A'], row['B'])

answered Feb 13 '23 at 04:28

Megatom

105
2

1

Thank you so much! This was just what I was looking for! Thank you everyone for their time and answers. This helps me a lot. – Joonatan Feb 13 '23 at 13:47

score 1 · Answer 2 · answered Feb 13 '23 at 05:19

I hope, it works for your solution. Whenever you have to apply a custom function and want to loop through values to perform an operation use apply function.

Code:

import pandas as pd
df = pd.read_csv('./loop_through_2_columns.csv')
def add_numbers(n1, n2):
    answer = n1+n2
    return answer
df['result'] = df.apply(lambda x: add_numbers(x.A, x.B), axis=1) 
df.head()

Output:

      A       B     result
0   232.65  -57.48  175.17
1   22.69   -5.46   17.23
2   23.67   -7.71   15.96

score 1 · Answer 3 · answered Feb 16 '23 at 06:10

try:

import pandas as pd

df = pd.DataFrame({
    'A': [232.65,22.69,23.67],
    'B':[-57.48,-5.46,-7.71]
})


def add_numbers(n1, n2):
    answer = n1+n2
    print(answer)

for i in range(len(df)):
    n1 = df.loc[i,'A']
    n2 = df.loc[i,'B']
    add_numbers(n1,n2)

output:

175.17000000000002
17.23
15.96

Python loop multiple positional arguments to function from dataframe or array

3 Answers3