On 5/12/2010 1:58 PM, Su Chu wrote:
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.
result = []
for n in list3:
result.append(sum(list1[x] for x in range(len(list1)) if list2[x] = n)
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.
--
Bob Gailer
919-636-4239
Chapel Hill NC
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