Hi there, I am new to Python. I am attempting to either define a "which" statement or to find a method that already exists to do this sort of operation.
My problem is as follows: I have three lists, one with unique values (list 1), one a sequence of values that are not necessarily unique (list2), and a shorter list with the unique values of list 2 (list 3). List 1 and List 2 are of equal lengths. An example: list1 = [ 1, 2, 3, 4, 5, 6 ] list2 = [ 2, 2, 2, 5, 6, 6 ] list3 = [2, 5, 6] What I would like to do is find and sum the elements of list 1 given its corresponding element in list 2 is equal to some element in list 3. For example, the sum of the values in list1 given list2[i]==2 would be 1 + 2 + 3 = 6. the sum of the values in list1 given list2[i]==5 would be 4 the sum of the values in list1 given list2[i]==6 would be 5 + 6 = 11 and so on. Obtaining these values, I'd like to store them in a vector. This seems pretty simple if a 'which' statement exists e.g. (which values in list 1 == list3[k], and looping through k), but I can't find one. To write one seems to require a loop. I'm at a loss, if you could help I'd really appreciate it!
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