Leading empty array elements after splitting

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

I'm attempting to extract numbers from codes in this generalised format (always begin with MD:Z: but what follows is variable):

MD:Z:4C3C7C0T2^T9C44

Desired output (separate array elements):

4
3
7
0
2
9
44
[download]

As I need to maintain positional information and length of each number (i.e. it must be clear that 44 = 44 and not the product of something like 4T4 after screening out letters) i've tried to use split:

my @test = split((/\D/g), $input);

To split on any non-number; however this returns a set of leading empty array values arising from the consecutive matches on 'MD:Z:'. Is there a way to suppress these or a better way to go about getting the desired result?

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Re: Leading empty array elements after splitting
by Athanasius (Archbishop) on Aug 22, 2016 at 15:26 UTC

If you use warnings, you’ll see that the /g modifier on the regex has no effect within a split. But why not keep the modifier, change \D to \d+, and dispense with split altogether?

 1:22 >perl -MData::Dump -wE "my $input = 'MD:Z:4C3C7C0T2^T9C44'; my @
+test = $input =~ /\d+/g; dd \@test;"
[4, 3, 7, 0, 2, 9, 44]

 1:22 >
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Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^2: Leading empty array elements after splitting

by Anonymous Monk on Aug 22, 2016 at 16:20 UTC

use warnings; use strict; Are always on for me - no warning was given, odd!

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Re^3: Leading empty array elements after splitting

by stevieb (Canon) on Aug 22, 2016 at 16:29 UTC

What version of Perl are you using (perl -v)?

On both 5.20.3 and 5.24.0, this code produces the following warning:

perl -wMstrict -E 'my @test = split((/\D/g), "x4d77");'

Use of /g modifier is meaningless in split at -e line 1.
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Re^4: Leading empty array elements after splitting

by Anonymous Monk on Aug 22, 2016 at 16:32 UTC

Re^5: Leading empty array elements after splitting

by stevieb (Canon) on Aug 22, 2016 at 17:00 UTC

Some notes below your chosen depth have not been shown here

Re: Leading empty array elements after splitting
by stevieb (Canon) on Aug 22, 2016 at 15:27 UTC

I'd use a global regex to extract just the digits directly into an array:

use warnings;
use strict;

my $string = 'MD:Z:4C3C7C0T2^T9C44';

my @nums = $string =~ /\d+/g;

print "$_\n" for @nums;
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Output:

4
3
7
0
2
9
44
[download]

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Re: Leading empty array elements after splitting
by TomDLux (Vicar) on Aug 23, 2016 at 16:01 UTC

Extracting just the numbers works well, but since you describe a problem with getting blank stuff you don't want, you might as well know about grep ...

22 11:56:12 tomdlux [ ~ ]
$ p522 -E 'say for split /\D+/, "MD:Z:4C3C7C0T2^T9C44"'               
+    

4
3
7
0
2
9
44
23 11:56:19 tomdlux [ ~ ]
$ p522 -E 'say for grep {length $_} split /\D+/, "MD:Z:4C3C7C0T2^T9C44
+"'  
4
3
7
0
2
9
44
[download]

As Occam said: Entia non sunt multiplicanda praeter necessitatem.

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