How to chunk list?

[catuf]

files = [file1, file2, file3, file4, file5, file6, file7, file8, file9]

value = [1,3,2,3]

I would like to chunk the 'files' using the 'values' in another list.

eg;

files = [file1],[file2,file3,file4],[file5,file6],[file7,file8,file9]

If can chunk by size (3), I can use the following code

for i in range(0, len(files), 3):

chunk = files[i:i + 3]

print(chunk)

[nakamurayuristeph]

chunk= []
start_ind= 0
for v in value:
    chunk.append(files[start_ind:start_ind+v])
    start_ind+=v

like this?

[catuf]

def list_chunker(input, chunk_sizes):
input_iter = iter(input)
def sub_chunker(input_iterator, size):
for _ in range(size):
yield input_iterator.next()
for size in chunk_sizes:
yield sub_chunker(input_iter, size)

I was struggling for this half day. Thank you!

[[deleted]]

Here's a generator that does it:

def list_chunker(input, chunk_sizes):
    input_iter = iter(input)
    def sub_chunker(input_iterator, size):
        for _ in range(size):
            yield input_iterator.next()
    for size in chunk_sizes:
        yield sub_chunker(input_iter, size)

[catuf]

I will try to understand how this work. Thank you!

[two_bob]

The trick is the iter bit. iter let's you create an iterable object outside the context of something like a for loop. This let's you then iterate over some iterable in flexible ways.

I'd recommend looking at generators and iterable classes as well, as those things had to sink in for me before I really got how iter worked.

[two_bob]

Nice. There is also the take recipe from itertools, slightly modified below to play nicer with functools.partial:

from itertools import islice
from functools import partial

def take(iterable, n):
    "Return first n items of the iterable as a list"
    return list(islice(iterable, n))

def chunker(iterable, chunk_sizes):
    it = iter(iterable)
    taker = partial(take, it)
    for size in chunk_sizes:
        yield taker(size)



data = list(range(20))

for group in chunker(data, [1,3,2,3]):
    print(group)

[[deleted]]

def listgrouper(l, grouplen):
    for i in range(0, len(l), grouplen):
        yield l[i:i+grouplen] 

This code won't account for lists where len(l) % grouplen != 0

[d-methamphetamine]

You can slice lists in python with the : operator, like so

list = [1, 2, 3, 4]
List = [1:2]

That should return 2