How to split existing list into smaller, separate lists (without using 'groupby')?

Question

I have a list with 64 values, that I want to split into 8 smaller lists. This is the function I used to make the values.

def listMaker(l):
    for i in range(10):
        l.append(f"0{i}") #Makes all singles digit numbers start with 0 ('01') to make grid even length
    
    for i in range(10, 64):
        l.append(f"{i}") #prints all numbers upto 63 (for index 0-63)

I want to go from: ['1','2','3','4']

To something like [['1','2']['3','4']]

So that it can be referenced like print(l[val1][val2])

What have you tried so far, and what went wrong with your attempts? For example, one place to start would be [Python-Understanding Slicing](https://stackoverflow.com/questions/509211/understanding-slicing) — G. Anderson, Dec 06 '22 at 20:11
See the `grouper` function in the `itertools` documentation, perhaps. — chepner, Dec 06 '22 at 20:14

score 2 · Accepted Answer · answered Dec 06 '22 at 20:10

2

You need to iterate over the main list, save the values into an intermediate list, when it reches the expected size, save it and use a new one

def listMaker(values, size):
    result, tmp = [], []
    for value in values:
        if len(tmp) == size:
            result.append(tmp)
            tmp = []
        tmp.append(value)

    if tmp:  # add last bucket
        result.append(tmp)
    return result


print(listMaker(range(10), 4))
# [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9]]
print(listMaker(range(20), 6))
# [[0, 1, 2, 3, 4, 5], [6, 7, 8, 9, 10, 11], [12, 13, 14, 15, 16, 17], [18, 19]]

answered Dec 06 '22 at 20:10

azro

53,056
7
34
70

I can see what the code means, but I don't understand what you mean by 'add last bucket'. I am not that familiar with the terminology of coding in general so if you could dumb it down a little bit that would be appreciated. – Manpreet Singh Dec 09 '22 at 22:03
@ManpreetSingh the loops only add each sublist when it's full, BUT as you can see in my examples, the last one may not be full, so it won't be added in the loop, you need a code that adds it it it is non-empty – azro Dec 10 '22 at 09:12

Treeco · Answer 2 · 2022-12-06T20:50:15.753

1

A list of sublists could be created with a list comprehension:

n = 8 #size of sublist
sublists = [l[x*n:x*n+n] for x in range(0, 8)]

edited Dec 06 '22 at 20:50

answered Dec 06 '22 at 20:14

Treeco

64
4

score 0 · Answer 3 · answered Dec 06 '22 at 20:27

You can use the "magic" zip-iter trick:

def listMaker(l):
    for i in range(10):
        l.append(f"0{i}") #Makes all singles digit numbers start with 0 ('01') to make grid even length
    
    for i in range(10, 64):
        l.append(f"{i}") #prints all numbers upto 63 (for index 0-63)

l = []

listMaker(l)

list2 = [list(subl) for subl in zip(*[iter(l)]*8)]

list2
# Out[133]: 
# [['00', '01', '02', '03', '04', '05', '06', '07'],
#  ['08', '09', '10', '11', '12', '13', '14', '15'],
#  ['16', '17', '18', '19', '20', '21', '22', '23'],
#  ['24', '25', '26', '27', '28', '29', '30', '31'],
#  ['32', '33', '34', '35', '36', '37', '38', '39'],
#  ['40', '41', '42', '43', '44', '45', '46', '47'],
#  ['48', '49', '50', '51', '52', '53', '54', '55'],
#  ['56', '57', '58', '59', '60', '61', '62', '63']]

How to split existing list into smaller, separate lists (without using 'groupby')?

3 Answers3