subset array with Fortran given a condition? -

suppose have array a(n,m). possible subset array in fortran create new array? example,

a = 11   22   43   55     15   56   65   63     54   56   32   78 

i want create array b m-1 columns , rows satisfies a(:,2) .eq. 56

so b should be:

b = 15   65   63     54   32   78 

i don't know how start because, example, dimension of b should determined dynamically (i think)

thanks help!

are looking this?

function extractb(a) result(b)     integer, dimension(:,:), intent(in) ::     integer, dimension(:,:), pointer :: b     integer :: nrowb, i, pos      nrowb = count( a(:,2)==56)     allocate( b(nrowb, size(a,2)-1 ) )     pos = 1     = 1, size(a,1)         if(a(i,2)==56)then             b(pos,1) = a(i,1)             b(pos,2:) = a(i,3:)             pos = pos+1         end if     end end function extractb 

that call like

b = extractb(a) 

with b defined like:

integer, dimension(:,:), allocatable :: b 

i assumed integer arrays. if compiler implement pointer return value, can used pointers in place of allocatable.

====adding full program ====

module extract contains      subroutine testextract(a, b)         double precision, dimension(:,:), intent(in)           ::         double precision, dimension(:,:), intent(out), allocatable :: b          b = extractb(a)       end subroutine testextract       function extractb(a) result(b)         double precision, dimension(:,:), intent(in) ::         double precision, dimension(:,:), allocatable :: b         integer :: nrowb, i, pos          nrowb = count( a(:,2)==56)         allocate( b(nrowb, size(a,2)-1 ) )         pos = 1         = 1, size(a,1)             if(a(i,2)==56)then                 b(pos,1) = a(i,1)                 b(pos,2:) = a(i,3:)                 pos = pos+1             end if         end     end function extractb end module extract  program test     use extract     integer, parameter :: n = 3     integer, parameter :: m = 4     double precision, dimension(3,4) ::     double precision, dimension(:,:), allocatable :: b       a(1,:) = [11,   22,   43,   55]     a(2,:) = [15,   56,   65,   63]     a(3,:) = [54,   56,   32,   78]      print*, 'a :'     print*, int(a)      !b = extractb(a)     call testextract(a, b)     print*, 'b'     print*, int(b)  end program