Creating a list within a list in Python

Question

I have a list named values containing a series of numbers:

values = [0, 1, 2, 3, 4, 5, ... , 351, 0, 1, 2, 3, 4, 5, 6, ... , 750, 0, 1, 2, 3, 4, 5, ... , 559]
         


        

Answer 1

This should work:

values = [0, 1, 2, 3, 4, 5, 351, 0, 1, 2, 3, 4, 5, 6, 750, 0, 1, 2, 3, 4, 5, 559]
new_values = []

split_at = 0  # split the list when this value is reached

idx = -1
for value in values:
    if value == split_at:
        idx += 1
        new_values.append([])

    new_values[idx].append(value)

Output:

[[0, 1, 2, 3, 4, 5, 351], [0, 1, 2, 3, 4, 5, 6, 750], [0, 1, 2, 3, 4, 5, 559]]

It also handles edgecasses.

My method is a bit faster than Chris_Rands's, but it's also a bit slower than Vasilis G's method:

from itertools import groupby


values = [
    0, 1, 2, 3, 4, 5, 351,
    0, 1, 2, 3, 4, 5, 6, 750,
    0, 1, 2, 3, 4, 5, 559,
]


def method1():
    new_values = []

    idx = -1
    for value in values:
        if value == 0:
            idx += 1
            new_values.append([])

        new_values[idx].append(value)

    return new_values


def method2():
    new_values = [[0] + list(g) for k, g in groupby(values, bool) if k]
    return new_values


def method3():
    indices = [index for index, value in enumerate(values) if value == 0] + [len(values)]
    new_values = [values[indices[i]:indices[i + 1]] for i in range(len(indices) - 1)]
    return new_values

---

>>> timeit.timeit(method1, number=100000)
0.6725746986698414
>>> timeit.timeit(method2, number=100000)
0.8143814620314903
>>> timeit.timeit(method3, number=100000)
0.6596001360341748