How to index an array with a mask in Fortran

Asked Feb 19 '14 at 15:31

Active Mar 08 '14 at 21:53

Viewed 177 times

I'm coming to Fortran from Python.

In Python / NumPy I can do the following:

import numpy as np
a = np.arange(5)
b = a*10

print b[a == 3]
#  Outputs: array([30])

In Fortran I have:

program test
implicit none

integer :: a(5)
integer :: b(5)
integer :: i

a = (/(i, i = 0, 4)/)
b = a*10

! I want to do this, but it doesn't work
!print *, b(a==3)

! So instead I do this...
do i=1,5
  if(a(i)==3) print*, b(i)
enddo

end

Is there a more elegant way of doing this (for example, with intrinsic functions)?

edited Mar 08 '14 at 21:53

Peter Mortensen

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asked Feb 19 '14 at 15:31

Pete W

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http://stackoverflow.com/q/21435589/3157076 – francescalus Feb 19 '14 at 15:36
Thanks @francescalus . The question was subtly different but the answer provided is what I need. print *, pack(b,a==3) is what I was looking for. – Pete W Feb 19 '14 at 15:49

How to index an array with a mask in Fortran

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