While loop within for loop for list of lists

Question

I'm trying to create a big list that will contain lists of strings. I iterate over the input list of strings and create a temporary list. Input:

['Mike','Angela','Bill','\n','Robert','Pam','\n',...]

My desired output:

[['Mike','Angela','Bill'],['Robert','Pam']...]

What i get:

[['Mike','Angela','Bill'],['Angela','Bill'],['Bill']...]

Code:

for i in range(0,len(temp)):
        temporary = []
        while(temp[i] != '\n' and i<len(temp)-1):
            temporary.append(temp[i])
            i+=1
        bigList.append(temporary)

stackoverflow.com/questions/4322705/… appears to be what you might want to look into. — StardustGogeta
– StardustGogeta, Commented Nov 27, 2017 at 2:19

Transhuman · Accepted Answer · 2017-11-27 02:20:05Z

3

Use itertools.groupby

from itertools import groupby
names = ['Mike','Angela','Bill','\n','Robert','Pam']
[list(g) for k,g in groupby(names, lambda x:x=='\n') if not k]
#[['Mike', 'Angela', 'Bill'], ['Robert', 'Pam']]

answered Nov 27, 2017 at 2:20

Transhuman

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Comments

cs95 · Accepted Answer · 2017-11-27 02:28:07Z

0

Fixing your code, I'd recommend iterating over each element directly, appending to a nested list -

r = [[]]
for i in temp:
    if i.strip():
        r[-1].append(i)
    else:
        r.append([])

Note that if temp ends with a newline, r will have a trailing empty [] list. You can get rid of that though:

if not r[-1]:
    del r[-1]

Another option would be using itertools.groupby, which the other answerer has already mentioned. Although, your method is more performant.

edited Nov 27, 2017 at 2:28

answered Nov 27, 2017 at 2:21

cs95

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Comments

Stephen · Accepted Answer · 2017-11-27 02:58:44Z

0

Your for loop was scanning over the temp array just fine, but the while loop on the inside was advancing that index. And then your while loop would reduce the index. This caused the repitition.

temp = ['mike','angela','bill','\n','robert','pam','\n','liz','anya','\n'] 
# !make sure to include this '\n' at the end of temp!
bigList = [] 

temporary = []
for i in range(0,len(temp)):
        if(temp[i] != '\n'):
            temporary.append(temp[i])
            print(temporary)
        else:
            print(temporary)
            bigList.append(temporary)
            temporary = []

answered Nov 27, 2017 at 2:58

Stephen

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Comments

SKN · Accepted Answer · 2017-11-27 04:55:54Z

0

You could try:

a_list = ['Mike','Angela','Bill','\n','Robert','Pam','\n']

result = []

start = 0
end = 0

for indx, name in enumerate(a_list):    
    if name == '\n':
        end = indx
        sublist = a_list[start:end]
        if sublist:
            result.append(sublist)
        start = indx + 1    

>>> result
[['Mike', 'Angela', 'Bill'], ['Robert', 'Pam']]

edited Nov 27, 2017 at 4:55

answered Nov 27, 2017 at 2:40

SKN

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