列表列表或多个列表可以元素组合的所有方式是什么 - 对每个列表中具有相同索引的项目进行操作？

Question

I have a list of lists and would like to operate on the items elementwise, combining items with the same index.

a = [[1,2,3],
     [4,5,6],
     [7,8,9]]

# or
b = [['1', '2', '3'],
     ['4', '5', '6'],
     ['7', '8', '9']]

Operate on a[0][i] , a[1][i] , a[2][i] .

new = [f(a[0][0],a[1][0]a[2][0]),
       f(a[0][1],a[1][1],a[2][1]),
       f(a[0][2],a[1][2],a[2][1])]

Where f is any function that accept appropriate arguments.

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Attempt to make a canonical for multiple similar questions. Feel free to add answers that I have overlooked.

Answer 1

Start by using zip to combine the items.

Multiple lists.

>>> list(zip(['1', '2', '3'], ['4', '5', '6'], ['7', '8', '9']))
[('1', '4', '7'), ('2', '5', '8'), ('3', '6', '9')]

Transposing a lists of list using zip(*thelist) - rows,columns -> columns,rows -

a = [[1,2,3],
     [4,5,6],
     [7,8,9]]

>>> list(zip(*a))
[(1, 4, 7),
 (2, 5, 8),
 (3, 6, 9)]

b = [['1', '2', '3'],
     ['4', '5', '6'],
     ['7', '8', '9']]

>>> list(zip(*b))
[('1', '4', '7'),
 ('2', '5', '8'),
 ('3', '6', '9')]

Once you have done that you can iterate and combine. All have a similar pattern: call a function/method passing the combined values.

Summing numbers

>>> [sum(thing) for thing in zip(*a)]
[12, 15, 18]
>>> list(map(sum, zip(*a)))
[12, 15, 18]

adding/concatenating/joining strings

>>> [''.join(thing) for thing in zip(*b)]
['147', '258', '369']
>>> list(map(''.join, zip(*b)))
['147', '258', '369']

Combining list of strings with list of numbers.

>>> x = ['a', 'b', 'c']
>>> y = [1,2,3]
>>> z = ['g', 'e', 'h']
>>> [''.join(str(item) for item in thing) for thing in zip(x,y,z)]
['a1g', 'b2e', 'c3h']
>>> [''.join(map(str,thing)) for thing in zip(x,y,z)]
['a1g', 'b2e', 'c3h']

Apply function to list of list elementwise.

>>> def f(args):
...     a,b,c,*_ = args
...     return (a+b)**c

>>> [f(thing) for thing in zip(*a)]
[78125, 5764801, 387420489]