comment on

Dear Monks,

I found on the perlfaq4 the following code:

use 5.010;
given( $number ) {
    when( /\D/ )
        { say "\thas nondigits"; continue }
    when( /^\d+\z/ )
        { say "\tis a whole number"; continue }
    when( /^-?\d+\z/ )
        { say "\tis an integer"; continue }
    when( /^[+-]?\d+\z/ )
        { say "\tis a +/- integer"; continue }
    when( /^-?(?:\d+\.?|\.\d)\d*\z/ )
        { say "\tis a real number"; continue }
    when( /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i)
        { say "\tis a C float" }
}
[download]

I am trying to find a way to determine the element from the array if it is an integer, decimal or float. But I am guessing that I am missing something.

I have modified the code for testing purposes:

#!/usr/bin/perl
use strict;
use warnings;

my @numbers = (1, -1, 123.1, 0.1);

foreach my $number (@numbers) {
    if ($number =~ /\D/ ) { 
    print "The $number has nondigits\n"; 
    }
    elsif ($number =~ /^\d+\z/ ) { 
    print "The $number is a whole number\n";
    }
    elsif ($number =~ /^-?\d+\z/ ) { 
    print "The $number is an integer\n"; 
    }
    elsif ($number =~ /^[+-]?\d+\z/ ) { 
    print "The $number is a +/- integer\n"; 
    }
    elsif ($number =~ /^-?(?:\d+\.?|\.\d)\d*\z/ ) { 
    print "The $number is a real number\n"; 
    }
    elsif ($number =~ /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i ) { 
    print "The $number is a C float\n"; 
    }
}
[download]

But I am getting, not the expected output:

The 1 is a whole number
The -1 has nondigits
The 123.1 has nondigits
The 0.1 has nondigits
[download]

I would expect something like:

The 1 is a +/- integer
The -1 is a +/- integer
The 123.1 is a C float
The 0.1 is a C float
[download]

Update: I was playing around to see if by modifying the numbers to string in the array will affect the output. I modified the my @numbers = (1, 1.0, 123.1, 0.1); to my @numbers = qw(1, 1.0, 123.1, 0.1);. That was the only modification that I applied and the output of the script changes only the first line The 1 is a whole number to The 1, has nondigits.

At this point I am sure that I am doing something completely wrong but I can not figure out what is it. Can someone help understand why I can not get the expected output?

Update 2: I also found from Is it a Number?.

my @numbers = ("1", "-1", "123.1", "0.1");

foreach my $number (@numbers) {
    my $integer = is_integer($number);
    print "$number is Integer\n" if ($integer);

    my $float = is_float($number);
    print "$number is Float\n" if ($float);
}

sub is_integer { $_[0] =~ /^[+-]?\d+$/ }
sub is_float   { $_[0] =~ /^[+-]?\d+\.?\d*$/ }

__END__

Output:

1 is Integer
1 is Float
-1 is Integer
-1 is Float
123.1 is Float
0.1 is Float
[download]

Update 3: As shmem pointed out, what I was afraid of, that regex compare against strings. So I guess the array to compare against should be modified to my @numbers = qw(1 1.0 123.1 0.1); as Laurent_R has pointed out. So the code should be like this:

#!/usr/bin/perl
use strict;
use warnings;

my @numbers = qw(1 -1 123.1 0.1 Characters);

foreach my $number (@numbers) {
    if ($number =~ /^[+-]?\d+\z/ ) { 
    print "The $number is a +/- integer\n"; 
    }
    elsif ($number =~ /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i ) { 
    print "The $number is a C float\n"; 
    }
    elsif ($number =~ /\D/ ) { 
    print "The $number has nondigits\n";
    }
}

__END__

The 1 is a +/- integer
The -1 is a +/- integer
The 123.1 is a C float
The 0.1 is a C float
The Characters has nondigits
[download]

Which starts to make more sense.

Update 4: An alternative and possibly better solution would be to use Switch. It will give us the same output.

#!/usr/bin/perl
use strict;
use warnings;

my @numbers = qw(1 -1 123.1 0.1 Characters);

foreach my $number (@numbers) {
    checkInputStringWithSwitchConditions($number);
}

sub checkInputStringWithSwitchConditions {
    use Switch;
    switch ($_[0]) {
    case /^[+-]?\d+\z/                         { print "The $_[0] is a
+ +/- integer\n" }
    case /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i { print "The $_[0
+] is a C float\n" }
    case /\D/                                        { print "The $_[0
+] has nondigits\n" }
    else                                         { print "Non of the c
+ases where True\n" }
    }
}

__END__

The 1 is a +/- integer
The -1 is a +/- integer
The 123.1 is a C float
The 0.1 is a C float
The Characters has nondigits
[download]

Update 5: By comparing the two methods together by using Benchmark, we can see that the Switch method is a better and faster method to use.

#!/usr/bin/perl
use strict;
use warnings;
use Benchmark qw( timethese cmpthese ) ;

my @numbers = qw(1 -1 123.1 0.1 Characters);

my $swithRefLoop = 'foreach my $number (@numbers) {
    checkInputStringWithSwitchConditions($number);
}';

my $ifAndElsIfRefLoop = 'foreach my $number (@numbers) {
    checkInputStringWithIfAndElseConditions($number);
}';

my $Benchmark = timethese( -10, {
    IfAndElsIfLoop => $ifAndElsIfRefLoop,
    SwitchLoop => $swithRefLoop,
               } );
cmpthese $Benchmark;

sub checkInputStringWithSwitchConditions {
    use Switch;
    switch ($_[0]) {
    case /^[+-]?\d+\z/                         { print "The $_[0] is a
+ +/- integer\n" }
    case /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i { print "The $_[0
+] is a C float\n" }
    case /\D/                                        { print "The $_[0
+] has nondigits\n" }
    else                                         { print "Non of the c
+ases where True\n" }
    }
}

sub checkInputStringWithIfAndElseConditions {
    if ( $_[0] =~ /^[+-]?\d+\z/ ) {
    print "The $_[0] is a +/- integer\n";
    }
    elsif ( $_[0] =~ /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i ) {
    print "The $_[0] is a C float\n";
    }
    elsif ( $_[0] =~ /\D/ ) {
    print "The $_[0] has nondigits\n";
    }
}

__END__

Benchmark: running IfAndElsIfLoop, SwitchLoop for at least 10 CPU seco
+nds...
IfAndElsIfLoop: 11 wallclock secs (10.04 usr + -0.00 sys = 10.04 CPU) 
+@ 4954765.54/s (n=49745846)
SwitchLoop:  9 wallclock secs (10.04 usr +  0.00 sys = 10.04 CPU) @ 56
+91789.84/s (n=57145570)
                    Rate IfAndElsIfLoop     SwitchLoop
IfAndElsIfLoop 4954766/s             --           -13%
SwitchLoop     5691790/s            15%             --
[download]

Thank you all for your time and effort reading and replying to my question.

Seeking for Perl wisdom...on the process of learning...not there...yet!

In reply to [SOLVED] How do I determine with a regular expression whether a scalar is a number/whole/integer/float? by thanos1983

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