作为列表列表的字典元素的总和

Question

d = {
  'a': [[1, 2, 3], [1, 2, 3]],
  'b': [[2, 4, 1], [1, 6, 1]],
}

def add_element(lst):
    ad = [sum(i) for i in zip(*lst)]
    return ad

def csv_reducer2(dicty):
    return {k: list(map(add_element, v)) for k, v in dicty.items()}

csv_reducer2(d)

required output:

{'b': [3, 10, 2], 'a': [2, 4, 6]}

Above is the code I have been trying but it gives an error

zip argument #1 must support iteration

Answer 1

>>> d = {'a': [[1, 2, 3], [1, 2, 3]], 'b': [[2, 4, 1], [1, 6, 1]]}
>>> {k: map(sum, zip(*v)) for k, v in d.items()}
{'a': [2, 4, 6], 'b': [3, 10, 2]}

Answer 2

The following will work on Python 2 or 3:

>>> {k: [a + b for a, b in zip(*v)] for k, v in d.items()}
{'a': [2, 4, 6], 'b': [3, 10, 2]}

The issue with your code is you are mapping add_element to every individual element in v inside your dictionary comprehension. This passes a one-dimensional list to zip in add_element , resulting in your error (since individual integers don't support iteration.

Answer 3

To fix your original code, the only change you need to make is:

return {k: list(map(add_element, v)) for k, v in dicty.items()}

->

return {k: add_element(v) for k, v in dicty.items()}

Because zip(*lst) is trying to transpose multiple rows into columns, but you are only passing it single rows through your original map