Fill a dataframe with the output of a loop-CodePudding

I'm trying to concatenate the output of a loop into dataframe. This example is totally unrealistic, but just to try to demonstrate my problem, my error and the result I need.

for a in range(1,4):

    list1 = ["22", "23", "24", "25"]
    list2 = ["a", "b", "c", "d"]
    
    df = pd.DataFrame({'Num': list1,'Alpha': list2})

    print(df)

My output:

Good output

   Num Alpha
0  22     a
1  23     b
2  24     c
3  25     d
4  22     a
5  23     b
6  24     c
7  25     d
8  22     a
9  23     b
10 24     c
11 25     d

CodePudding user response：

This is one way to do it using your code above. Create an empty list before your for loop and append the df to it. Then concat the final list.

l = []   

for a in range(1,4):
    list1 = ["22", "23", "24", "25"]
    list2 = ["a", "b", "c", "d"]
    
    df = pd.DataFrame({'Num': list1,'Alpha': list2})

    l.append(df)

df = pd.concat(l)

CodePudding user response：

Use pd.concat with *3 instead of looping through a range of 3:

import pandas as pd
list1 = ["22", "23", "24", "25"]
list2 = ["a", "b", "c", "d"]
df = pd.concat([pd.DataFrame({'Num': list1,'Alpha': list2})] * 3).reset_index(drop=True)
df
Out[1]: 
   Num Alpha
0   22     a
1   23     b
2   24     c
3   25     d
4   22     a
5   23     b
6   24     c
7   25     d
8   22     a
9   23     b
10  24     c
11  25     d

CodePudding user response：

You can do

l = []
for a in range(1, 4):
    
    list1 = ["22", "23", "24", "25"]
    list2 = ["a", "b", "c", "d"]
    l.append(pd.DataFrame({'Num': list1, 'Alpha': list2}))
out = pd.concat(l,ignore_index = True)