splitting list into smaller lists

Question

def group(l,size):
    length = len(l)
    new = []
    for i in range(0,length):
        for j in range(i,size):
            new[i].append(l[j])
    print new

The above function group(list, size) that take a list and splits into smaller lists of given size.

I need something like this

input: group([1, 2, 3, 4, 5, 6, 7, 8, 9], 3)
output: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

But the problem with the above code is showing index out of range.what's wrong in code? how to append elements into list of lists?

You're going to need to be very explicit with this question as it could be (and I have) mistaken it for [this very often asked one](http://stackoverflow.com/questions/312443/how-do-you-split-a-list-into-evenly-sized-chunks-in-python). Are you 1) After a way to group data in groups of various size, or 2) **After help correcting your posted code** - You may wish to [edit] your question accordingly to state if it is indeed number 2 to avoid potential confusion. — Jon Clements, Jun 27 '13 at 06:53

score 6 · Accepted Answer · answered Jun 27 '13 at 06:47

6

Use slice.

>>> def group(l, size):
...     return [l[i:i+size] for i in range(0, len(l), size)]
... 
>>> group([1, 2, 3, 4, 5, 6, 7, 8, 9], 3)
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

answered Jun 27 '13 at 06:47

falsetru

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score 0 · Answer 2 · edited May 23 '17 at 12:28

0

try:

def group(l,size):
    length = len(l)
    new = []
    for i in range(0, length/size):
        new.append([])
    for i in range(0,len(new)):
        for j in range(i*size,(i*size)+size):
            new[i].append(l[i+j])
    print new

edit: no, don't do this. use slice like falsetru illustrates.

edited May 23 '17 at 12:28

Community

1
1

answered Jun 27 '13 at 06:39

Matthew Graves

3,226
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score -1 · Answer 3 · answered Jun 27 '13 at 06:46

rough solution would be this :]

def group(l,size):
    length = len(l)
    newlist = []
    newgroup = []
    j = 0
    for i in range(0,length):
        if(j<size - 1):
            j += 1
            newgroup.append(l[i])
        else:
            j = 0
            newgroup.append(l[i])
            newlist.append(newgroup)
            newgroup = []
    if(newgroup != []):
        newlist.append(newgroup)
    return newlist

print(group([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], 3))

result: [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11]]

why -1? I didn't test, but if it yields the given result, it seems a valid solution. (but a quite complicated one) — glglgl, Jun 27 '13 at 07:10

splitting list into smaller lists

3 Answers3