Creating New Column in Pandas Data frame with For Loop Issue

Question

I am trying to compare two columns (key.response and corr_answer) in a csv file using pandas and creating a new column "Correct_or_Not" that will contain a 1 in the cell if the key.response and corr_answer column are equal and a 0 if they are not. When I evaluate on their own outside of the loop they return the truth value I expect. The first part of the code is just me formatting the data to remove some brackets and apostrophes.

I tried using a for loop, but for some reason it puts a 0 in every column for 'Correct_or_Not".

import pandas as pd
df= pd.read_csv('exptest.csv')
df['key.response'] = df['key.response'].str.replace(']','')
df['key.response'] = df['key.response'].str.replace('[','')
df['key.response'] = df['key.response'].str.replace("'",'')
df['corr_answer'] = df['corr_answer'].str.replace(']','')
df['corr_answer'] = df['corr_answer'].str.replace('[','')
df['corr_answer'] = df['corr_answer'].str.replace("'",'')

for i in range(df.shape[0]):
    if df['key.response'][i] == df['corr_answer'][i]:
        df['Correct_or_Not']=1
    else: 
        df['Correct_or_Not']=0

df.head()

  key.response corr_answer Correct_or_Not
0   1              1            0
1   2              2            0
2   1              2            0

the problem is df['Correct_or_Not']=1 creates a new column of 1s from scratch each time (same with df['Correct_or_Not']=0) — Dan
– Dan, Commented Nov 12, 2019 at 15:09

mcsoini · Accepted Answer · 2019-11-12 15:14:30Z

2

You can generate the Correct_or_Not column all at once without the loop:

df['Correct_or_Not'] = df['key.response'] == df['corr_answer']

and df['Correct_or_Not'] = df['Correct_or_Not'].astype(int) if you need the results as integers.

In your loop you forgot the index [i] when assigning the result. Like this the last row's result gets applied everywhere.

answered Nov 12, 2019 at 15:14

mcsoini

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Comments

Carlz Karthik · Accepted Answer · 2019-11-12 16:09:52Z

0

you can also do this

df['Correct_or_not']=0
    for i in range(df.shape[0]):
        if df['key.response'][i]==df['corr_answer'][i]:
            df['Correct_or_not'][i]=1

answered Nov 12, 2019 at 16:09

Carlz Karthik

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