use threshold on a list of numbers to subset corresponding elements from other list of objects-CodePudding

I have two lists of lists which share the same dimension (same length, each list in the list have the same number of elements)

list1 looks like this:

list1 = [[1,2,3],[2,3,4],[4,5,2],[4,0,9]]

list2 looks like this:

list2 = [['a''b','c'],['a','d','e'],['a','f','b'],['p','o','a']]

let's say I have a threshold x = 3

I want to filter out elements from list 2 which have the same position of those elements in list1 which fall below x = 3

so for instance for x = 3 I would want to obtain:

list3 = [[],['e'],['a','f'],['p','a']

how can I do so?

thank you for your help

CodePudding user response：

You can use zip to walk the two lists (and sublists) together and filter the values in list2 that satisfy the condition in the corresponding position in list1:

out = [[j for i, j in zip(li1, li2) if i>3] for li1, li2 in zip(list1, list2)]

Output:

[[], ['e'], ['a', 'f'], ['p', 'a']]

CodePudding user response：

I would use the Python zip function to "merge" the two lists.

list1 = [[1,2,3],[2,3,4],[4,5,2],[4,0,9]]
list2 = [['a','b','c'],['a','d','e'],['a','f','b'],['p','o','a']]

threshold = 3

list3 = [
    [char for value, char in zip(sub_one, sub_two) if value > threshold]
    for sub_one, sub_two in zip(list1, list2)
]

print(list3)

This outputs

[[], ['e'], ['a', 'f'], ['p', 'a']]

The outer zip merges list1 and list2 into:

[([1, 2, 3], ['a', 'b', 'c']),
 ([2, 3, 4], ['a', 'd', 'e']),
 ([4, 5, 2], ['a', 'f', 'b']),
 ([4, 0, 9], ['p', 'o', 'a'])]

while the inner zip merges e.g. [1,2,3] and ['a','b','c'] into [(1, 'a'), (2, 'b'), (3, 'c')]. Then, the inner list comprehension can use a simple filtering with if value > threshold.