How to add an array with using Python

Question

Given an array a = [1,2,3,[4,5]] using Python 3, how can I add all the elements in the array?

sum(a[0])
sun(a[0][1])

The above code did not work. Also in the case, if you're given an array with an unknown amount of arrays inside arrays, How can those numbers be calculated?

You can use len(array) to find the number of elements inside. — Alfie
– Alfie, Commented Jul 26, 2018 at 13:41
Terminology nitpick: arrays and lists are different things. arrays can only contain certain types of objects, and they can't contain other arrays. — Kevin
– Kevin, Commented Jul 26, 2018 at 13:43

user3278460 · Accepted Answer · 2018-07-26 15:41:15Z

3

def xsum(x):
    if not x:
        return 0

    head, *tail = x

    if isinstance(head, list):
        return xsum(head) + xsum(tail)
    elif tail:
        return head + xsum(tail)
    else:
        return head

answered Jul 26, 2018 at 15:41

user3278460

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Comments

FHTMitchell · Accepted Answer · 2018-07-26 13:49:24Z

2

You need a flatten function. Here is one:

def flatten(a):
    """generator of flattened n-deep iterable (excluding str) a."""
    for elem in a:
        if not isinstance(elem, str):
            try:
                yield from flatten(elem)
            except TypeError:
                yield elem
        else:
            yield elem

which you can then use in sum, for example:

a = [1, 2, 3, [4, [5, 6]]
print(list(flatten(a)))  # --> [1, 2, 3, 4, 5, 6]
print(sum(flatten(a)))  # --> 21

edited Jul 26, 2018 at 13:49

answered Jul 26, 2018 at 13:43

FHTMitchell

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Comments

Sunitha · Accepted Answer · 2018-07-26 13:47:43Z

0

You can use functools.reduce to sum this nested list

>>> from functools import reduce
>>> a = [1,2,3,[4,5]] 
>>> reduce(lambda x,y: x + (sum(y) if type(y)==list else y), [0]+a)
15

If the list can be more than one level nested, you have to use a recursive approach

>>> f = lambda x,y: x + (reduce(f, y) if type(y)==list else y)
>>> reduce(f, [0]+a)
15

answered Jul 26, 2018 at 13:47

Sunitha

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Comments

utks009 · Accepted Answer · 2018-07-26 14:15:59Z

0

You can use the closure property for finding sum of infinite nested list.

def nested_list_sum(x):
c = []

def l_sum(x):
    for i in x:
        if isinstance(i, list):
            l_sum(i)
        else:
            c.append(i)
l_sum(x)
return sum(c)

like a = [1,2,3,[4,5]] ----> 15

a = [1,2,3,[4,5, [6,7, [8, 9]]], [10, 11, 12, [13, 14, 5]]] -- > 110

answered Jul 26, 2018 at 14:15

utks009

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