python union of 2 nested lists with index
- by sbas
I want to get the union of 2 nested lists plus an index to the common values.
I have two lists like A = [[1,2,3],[4,5,6],[7,8,9]] and B = [[1,2,3,4],[3,3,5,7]] but the length of each list is about 100 000. To A belongs an index vector with len(A): I = [2,3,4]
What I want is to find all sublists in B where the first 3 elements are equal to a sublist in A. In this example I want to get B[0] returned ([1,2,3,4]) because its first three elements are equal to A[0]. In addition, I also want the index to A[0] in this example, that is I[0].
I tried different things, but nothing worked so far :(
First I tried this:
Common = []
for i in range(len(B)):
if B[i][:3] in A:
id = [I[x] for x,y in enumerate(A) if y == B[i][:3]][0]
ctdCommon.append([int(id)] + B[i])
But that takes ages, or never finishes
Then I transformed A and B into sets and took the union from both, which was very quick, but then I don't know how to get the corresponding indices
Does anyone have an idea?
