Removing the last element of a list: Why does ".pop() not work?-CodePudding

I am working on a test dataset which is

print(df.head(10))

0                   NaN
1     93/2; 99/3; 05/4;
2                   NaN
3                   NaN
4                   NaN
5                   NaN

Now i want to convert the string "93/2; 99/3; 05/4;" to a more neat data structure for following analysis. Thus the first step would be so split on the ";"

df= df.apply(lambda x: x.split(';'))

which yields

0                        []
1    [93/2,  99/3,  05/4, ]
2                        []
3                        []
4                        []
5                        []
6                        []
7                        []
8                        []
9                        []

As you see the last element of the list is an empty value, which i want to delete. I was thinking about using the .pop() function but that yields

df = df.apply(lambda x: x.pop())
print(df.head(10))

0    
1    
2    
3    
4    
5    
6    
7    
8    
9

if i am using slicing

df = df.apply(lambda x: x[:-1])

i get the expected output

0                      []
1    [93/2,  99/3,  05/4]
2                      []
3                      []
4                      []
5                      []
6                      []
7                      []
8                      []
9                      []

Could anyone please explain why the pop function is not working here as i expected?

Thank you in advance!

CodePudding user response：

It works. You assign the return of pop() back into your df. pop() returns the element that gets popped. You assign that element to your df.

CodePudding user response：

There is a vectorial function to split strings str.split, and one to strip characters:

Assuming a dataframe here, although your example might indicate you have a Series:

                # strip trailing ;   # split on ;
df['lst'] = df['col'].str.rstrip(';').str.split(';\s*')

if Series:

ser2 = ser.str.rstrip(';').str.split(';\s*')

output:

                 col                 lst
0                NaN                 NaN
1  93/2; 99/3; 05/4;  [93/2, 99/3, 05/4]
2                NaN                 NaN
3                NaN                 NaN
4                NaN                 NaN
5                NaN                 NaN