Iterate over array twice (cartesian product) but consider only half the elements

Question

I am trying to iterate over an array twice to have pairs of elements (e_i,e_j) but I only want the elements such that i < j.

Basically, what I want would look lik

Answer 1

I would suggest the following:

midIdx = len(mylist) / 2
[ dosomehing(ele_i, ele_j) for ele_i, ele_j in 
    zip( mylist[0:midIdx], mylist[midIdx + 1:len(mylist)] ) ]

For most interpreted language, for loop is not the best choice. Python provides list comprehension, which is more readable and efficient.

Answer 2

Can't you just use the range function and go with:

vect = [...]
for i in range(0, len(vect)):
    for j in range(i+1, len(vect)):
        do_something()

Answer 3

Just use itertools.combinations(my_list, 2).