Passing Lists to Functions?

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I am trying to pass a two dimensional array (or a list of references you may say) along with some numbers into a function in the following way:

@reduced_protein = shift (\@reduced_protein,($x2-$x1),($y2-$y1),($z2-$
+z1)); 

# reduced protein is 2D array with each line having some properties ab
+out the protein. The shift function just shifts the coordinates of th
+e all lines thus the protein (given below)

sub shift 
        {
        my ($reduced_protein, $shift_x, $shift_y, $shift_z);
        my @reduced_protein=@$reduced_protein;
        my $index1;
        my $protein_length=findColumnLength(@reduced_protein);
        
        for ... (shifting operation)
return @reduced_protein;
}
[download]

This gives the error "Type of arg 1 to shift must be array (not list)..." how do we pass such a list to a function? Thanks for the help

Comment on Passing Lists to Functions? Download Code

Replies are listed 'Best First'.
Re: Passing Lists to Functions? by RMGir (Prior) on May 16, 2008 at 22:48 UTC
shift is a built-in function :) Try calling your function shiftProtein, and see what happens... Mike	[reply]
Re: Passing Lists to Functions? by johngg (Canon) on May 16, 2008 at 22:57 UTC
Also note that arguments are passed into subroutines in the array `@_` so you need to populate your variables from that. It might also be an idea to change the name of the array reference to avoid confusion. `sub shiftProtein { my ( $ref_to_reduced_protein, $shift_x, $shift_y, $shift_z ) = @_; my @reduced_protein = @$ref_to_reduced_protein; ...` [download] I hope this is of use. Cheers, JohnGG	[reply] [d/l] [select]
Re: Passing Lists to Functions? by pc88mxer (Vicar) on May 16, 2008 at 22:49 UTC
You should avoid using `shift` as the name of a subroutine. In this call: `@reduced_protein = shift (\@reduced_protein,($x2-$x1),($y2-$y1),($z2-$ +z1));` [download] perl thinks you want the built-in shift function which takes an array (not an array ref) as the first argument. Just rename your subroutine to something else, or qualify it with `::`: `some_package::shift(\@reduced_protein, ...);` [download]	[reply] [d/l] [select]
Re: Passing Lists to Functions? by mwah (Hermit) on May 17, 2008 at 12:14 UTC
The most significant error (shift as a sub) has been already mentioned. (Put a large 'S' as the first char if you need to name it that way). I'd like to make a comment to other aspects of your code. If you give a reference to something into a sub, this (referenced) object will be modified, so you won't need to copy it back and forth. ... # the array will be modified 'in place', so theres # no necessity to copy stuff around Shift( \@reduced_protein, $x2-$x1, $y2-$y1, $z2-$z1 ); ... sub Shift { my ($rp_ref, $x, $y, $z) = @_; # traditional way to feed a sub my $index1; # the expression @$array_ref expands a reference to a list my $protein_length = findColumnLength(@$rp_ref); for (shifting operation) { ... # instead of: $reduced_protein[i], # you say: $rp_ref->[i] ... } # no need to return anything, the original array is # already modified } [download] Regards mwa	[reply] [d/l]


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