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

Dear Monks,

I have a subroutine like: 


sub correlation {

  print "\nWe are in the correlation subroutine\n\n";

  my ($x_ref, $y_ref) = @_;     

  
  
  my @x = @{$x_ref};

  my @y = @{$y_ref}; 


  my $lfit = Statistics::LineFit->new();
  $lfit->setData(@x, @y);
  
  printf "a=%.4f, b=%.4f,  R2=%.4f\n", $lfit->coefficients(), $lfit->r
+Squared();
  
  
  return  "a=%.4f, b=%.4f, R2=%.4f\n", $lfit->coefficients(), $lfit->r
+Squared();

}

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This sub is activated like: 

my ($y_axis_intercept, $gradient, $R2) = correlation(\@primarys, \@sec
+ondarys);

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The error message that I get is: 

Can't use an undefined value as an ARRAY reference at c:/Perl/site/lib
+/Statistic
s/LineFit.pm line 191, <DATA> line 164.

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Replies are listed 'Best First'.
Re: LineFit.pm error due to undef value
by jdporter (Paladin) on Nov 20, 2007 at 15:44 UTC

    RTFM! 

    $lineFit->setData(\@x, \@y)

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    Explaining why it should be like this is something probably best left to the tutorials.

    A word spoken in Mind will reach its own level, in the objective world, by its own weight
[reply]
[d/l]

      I'll add (thought I expect this will go right over your head) that you don't even need to deref and reref the arrays: 

      sub correlation
{
  . . .
  my( $x_ref, $y_ref ) = @_;     
  my $lfit = Statistics::LineFit->new();
  $lfit->setData( $x_ref, $y_ref );
  . . .
}

      [download]
[reply]
[d/l]
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