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Sorting (big) int array: Eliminate for loop [message #68062]

Mon, 21 September 2009 07:46

Luds
Messages: 7
Registered: September 2009

Junior Member

Hi,
I'm trying to eliminate a for loop form one of my codes, but can't
seem to get around it (though I must be able to, with the histogram
function, or something of the sort)... I was hoping to get some advice
from the (semi-)pros.

Here's what I want to do:
I have two arrays, A & B. Both are sparse and contain non-contiguous
integers. Both are 1-dimensional and have the same number of elements.
Array B contains all the same values as array A, but in a random
order. I want to find the elements with which I can subscript array B
so that it returns A (i.e. I want B(elements)=A).

Trivially I get what I want with

For K = 0L, Narray - 1L do elements[K] = where(B eq A[K])

The arrays contain 10's of millions of elements, so memory is an
issue.... but clearly a For loop is WAY to slow and I'm crazy for even
considering it as an option.

Does anyone have any advice on this?

Thanks 10's of millions!

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Sorting (big) int array: Eliminate for loop

By: Luds on Mon, 21 September 2009 07:46

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