Re^4: question about what to grep(?)

I got an uninitialized variable error the way you had it so I added the foreach bit here, & also changed the round to int(). I got your idea:

sub is_approximately_an_integer {
    foreach my $x ( @zeros ) {
    $x = shift;
    my $eps = 0.0001;
    return abs( $x-int($x) ) < $eps;
    }
}
[download]

It seems to work ok like that. I guess next is to use the subroutine with $_ inside grep somehow?

my @wants = grep { } values %haystack;

Comment on Re^4: question about what to grep(?) Select or Download Code

Replies are listed 'Best First'.
Re^5: question about what to grep(?) by hdb (Monsignor) on Apr 13, 2013 at 08:30 UTC
As always, there is more than one way to do it. Please see code below for some illustrations. Some comments: Using @zeros in the sub is a bad idea. All numbers to be tested should be passed as arguments, see below. I had not mentioned this. "int" only cuts of digits. So int(2.9999) is 2 which is not what you want. One can use it for rounding, but it is more complex and there is a module doing it for us: Math::Round. I have illustrated the use of our test function with a few examples below. In grep you can iterate either over your keys or over the arrays, you just need to call the test function appropriately. As you are iterating over all elements of the hash, speed of lookup is not an issue in my opinion. Hope this helps. use strict; use warnings; use Math::Round qw/round/; use Data::Dumper; # function returns 1 if all arguments are integer # zero otherwise sub is_approximately_an_integer { my $eps = 0.0001; while( my $x = shift ) { # need to use "round", "int" does not work! return 0 if abs( $x-round($x) ) > $eps; } return 1 } # some test cases print "Testing...\n"; print is_approximately_an_integer( 1, 3.99999999, 5 ), "\n"; print is_approximately_an_integer( 1.2, 3.99999999, 5 ), "\n"; print is_approximately_an_integer( 1, 3.99999999, 5.0000001 ), "\n"; print is_approximately_an_integer( 1, 3.99999999, -5 ), "\n"; print is_approximately_an_integer( 1, 3.99999999, -5.1 ), "\n"; print is_approximately_an_integer( 1, 3.99999999, -5.000000001 ), "\n" +; print is_approximately_an_integer( 1, -3.99999999, -5.000000001 ), "\n +"; print is_approximately_an_integer( 1 ), "\n"; print is_approximately_an_integer( 1.5 ), "\n"; # what if we have hash of arrays ? my %hash = ( "1,2,3" => [ 1, 3.99999999, 5 ], "1,2,4" => [ 1.2, 3.99999999, 5 ], "1,2,5" => [ 1, 3.99999999, 5.0000001 ], # etc ); # this returns only the arrays but lose keys print "\nSelected arrays\n"; my @wants = grep { is_approximately_an_integer( @$_ ) } values %hash; print Dumper( @wants ); # this returns the keys print "\nSelected keys...\n"; my @wants = grep { is_approximately_an_integer( @{$hash{$_}} ) } keys +%hash; print Dumper( @wants ); print "...and the associated array.\n"; # and you can get the arrays as well print Dumper( @hash{@wants} ); [download]	[reply] [d/l]

Replies are listed 'Best First'.

Re^5: question about what to grep(?)
by hdb (Monsignor) on Apr 13, 2013 at 08:30 UTC

As always, there is more than one way to do it. Please see code below for some illustrations. Some comments:

Using @zeros in the sub is a bad idea. All numbers to be tested should be passed as arguments, see below. I had not mentioned this.
"int" only cuts of digits. So int(2.9999) is 2 which is not what you want. One can use it for rounding, but it is more complex and there is a module doing it for us: Math::Round.
I have illustrated the use of our test function with a few examples below.
In grep you can iterate either over your keys or over the arrays, you just need to call the test function appropriately.
As you are iterating over all elements of the hash, speed of lookup is not an issue in my opinion.

use strict;
use warnings;
use Math::Round qw/round/;
use Data::Dumper;

# function returns 1 if all arguments are integer
# zero otherwise
sub is_approximately_an_integer {
  my $eps = 0.0001;
  while( my $x = shift ) {
    # need to use "round", "int" does not work!
    return 0 if abs( $x-round($x) ) > $eps;
  }
  return 1
}

# some test cases
print "Testing...\n";
print is_approximately_an_integer( 1, 3.99999999, 5 ), "\n";
print is_approximately_an_integer( 1.2, 3.99999999, 5 ), "\n";
print is_approximately_an_integer( 1, 3.99999999, 5.0000001 ), "\n";
print is_approximately_an_integer( 1, 3.99999999, -5 ), "\n";
print is_approximately_an_integer( 1, 3.99999999, -5.1 ), "\n";
print is_approximately_an_integer( 1, 3.99999999, -5.000000001 ), "\n"
+;
print is_approximately_an_integer( 1, -3.99999999, -5.000000001 ), "\n
+";
print is_approximately_an_integer( 1 ), "\n";
print is_approximately_an_integer( 1.5 ), "\n";

# what if we have hash of arrays ?
my %hash = (
        "1,2,3" => [ 1, 3.99999999, 5 ],
        "1,2,4" => [ 1.2, 3.99999999, 5 ],
        "1,2,5" => [ 1, 3.99999999, 5.0000001 ],
        # etc
);

# this returns only the arrays but lose keys
print "\nSelected arrays\n";
my @wants = grep { is_approximately_an_integer( @$_ ) } values %hash;
print Dumper( @wants );

# this returns the keys
print "\nSelected keys...\n";
my @wants = grep { is_approximately_an_integer( @{$hash{$_}} ) } keys 
+%hash;
print Dumper( @wants );
print "...and the associated array.\n";
# and you can get the arrays as well
print Dumper( @hash{@wants} );
[download]

[reply]
[d/l]