Re: Arrays Intersection
- From: Arjen Markus <arjen.markus@xxxxxxxxxx>
- Date: Fri, 30 May 2008 05:53:27 -0700 (PDT)
On 30 mei, 13:34, Infinity77 <andrea.gav...@xxxxxxxxx> wrote:
Hi All,
I have received so many nice answers in this newsgroup that I
thought I could ask one more question. I am trying to find the
intersection of 2 one-dimensional integer arrays, where "intersection"
means the common elements in both arrays, i.e.:
a = [1,2,3,4,5,6]
b = [5, 6, 7]
intersection(a, b) ==> [5, 6]
At the moment I am working with Python, which handles very well sets,
lists and structures for which it's easy to define an "intersection",
but as I have many many arrays to compare, this is becoming a bit slow
so I thought to use fortran. Unfortunately, my google-fu failed me as
I couldn't find anything related to "array intersection" in Fortran.
Does anyone know what I should do in order to achieve a fast solution
to this problem?
Thank you very much for your suggestions.
Andrea.
You might use:
pack( array1, (/ (any(array1(i) == array2), i=1,size(array1)) /) )
Tis may require some explanation:
- (/ ... /) is an array constructor
- in this statement it constructs an array of logical
values where the value is true if the element from the
first array coincides with one from the other
- the result is used to extract (via pack()) only those
elements for which that condition holds.
Here is your example:
program intersect
integer, dimension(6) :: array1 = (/ 1, 2, 3, 4, 5, 6 /)
integer, dimension(3) :: array2 = (/ 5, 6, 7 /)
integer :: i
write(*,*) &
pack( array1, (/ (any(array1(i) == array2), i=1,size(array1)) /) )
end program
One tricky thing though:
As you do not know in advance how large this resulting array
is, you can best pass it on to a subroutine:
subroutine copy( array, result )
integer, dimension(:) :: array
integer, dimension(:), pointer :: result
allocate( result(1:size(array)) )
result => array
end subroutine
as otherwise you have to compute the size in advance and
allocate an array of that size.
Regards,
Arjen
.
- Follow-Ups:
- Re: Arrays Intersection
- From: Gordon Sande
- Re: Arrays Intersection
- References:
- Arrays Intersection
- From: Infinity77
- Arrays Intersection
- Prev by Date: Re: Is this legal?
- Next by Date: Re: one-liner for characater replacement
- Previous by thread: Arrays Intersection
- Next by thread: Re: Arrays Intersection
- Index(es):
Relevant Pages
|
|
