CODEWITHSUNDEEP
pythonlist
nam
nam

Reputation: 215

Do sum in a nested list of a given list

Than I want to write a function that achieves this purpose, if given:

t = [1,2,[2,2],[3,3]]

I want a function that makes t be [1,2,4,6]. Here, is my code in Python:

t=[1,2,[2,2],[3,3]]

def nested_sum(t):
    for x in t:
        if type(t[x])=='int':
            t[x]=t[x]
        else:
            t[x]=['sum(t[x])']
    return t

nested_sum(t)

I got the error message that

Traceback (most recent call last):
  File "nested_sum.py", line 11, in <module>
    nested_sum(t)
  File "nested_sum.py", line 5, in nested_sum
    if type(t[x])=='int':
TypeError: list indices must be integers, not list

I am not quite sure about the mistake(s) I made. Since my logic is that:

type(t[0])=1 which is of "Int" type and type(t[2])=[2,2] which is of "List" type and I think these fulfills the "if...else..." statement.

Any help would be appreciated for pointing my mistakes. Thank you so much in advance.

Upvotes: 0

Views: 446

Answers (5)

Railslide
Railslide

Reputation: 5564

The problem with your code is that you are looping through the items of your list and not through the indexes. For making it work you should change your code like this:

def nested_sum(t):
    for x in range(len(t)):
        if type(t[x]) == int:
            t[x] = t[x]
        else:
            t[x] = sum(t[x])
    return t

Note also that int in type(t[x]) == int and sum(t[x]) in your else clause should not be strings.

Upvotes: 0

Padraic Cunningham
Padraic Cunningham

Reputation: 180512

You can put it in a single list comprehension using isinstance:

[sum(x) if isinstance(x,list) else x for x in t]

[1, 2, 4, 6]

You could use collection.Iterable which will work on any iterable like tuples etc..

t = [1,2,[2,2],[3,3],(4,5)]

from collections import Iterable

print [sum(x) if isinstance(x, Iterable) else x for x in t]

[1, 2, 4, 6, 9]

In the list comprehension, if x is an iterable/list we add the sum of the subelements or else we just take the element x

Using your own code, you would use enumerate to access the list elements using their index:

def nested_sum(t):
    for ind, x in enumerate(t):
        if type(t[ind])== int: # int not "int"
            t[ind] = x
        else:
            t[ind] = sum(t[ind])
    return t

In the code ind is the index of each subelement and x is the actual subelement

Upvotes: 4

RickardSjogren
RickardSjogren

Reputation: 4238

An answer would be:

def nested_sum(mixed_list):
    res = list()
    for element in mixed_list:
        try:
            a = sum(element)
        except TypeError:
            a = element
        res.append(a)
    return res

Which works fine if the list contains numbers and lists of numbers.

Upvotes: 0

Saimadhav Heblikar
Saimadhav Heblikar

Reputation: 712

def nested_sum(t):
    for index, item in enumerate(t):
        if type(item) == list:
            t[index] = sum(item)
    return t

Explanation:

enumerate(t) returns (0, t[0]), (1, t[1]) etc.

Then, for each item in t, check if item is a list. If it is, replace it with the sum of all elements in that list. This is done in t[index] = sum(item).

Upvotes: 0

xecgr
xecgr

Reputation: 5193

Use sum() when x is a list, append it to res otherwise

t=[1,2,[2,2],[3,3]]

def nested_sum(l):
    res = []
    for x in l:
        if type(x) == type([]):
            res.append(sum(x))
        elif type(x) == type(1):
            res.append(x)
    return res

nested_sum(t)

Upvotes: 0

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