Is Array Element Numeric? (was I wonder...)

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

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Re: Is Array Element Numeric? (was I wonder...) by LTjake (Prior) on Aug 22, 2002 at 11:39 UTC
Use a regex. `if ($array[0] =~ /^\d+$/) { # do something }` [download] ^ signifies the start of the string \d means a digit + means match 1 or more times $ signifies the end of the string Update: you can also add `[+-]?` right after `^` if your numbers can have prefixes. Also, see this page: Is it a number? Update 2: Yes, there are obvious loopholes, Anonymous Monk, such as decimal numbers (they didn't specify what they were matching exactly. just "numeric values"). See the link above (is it a number?) for more robust solutions. Here's a snippet of some nice functions from it: `sub is_whole_number { $_[0] =~ /^\d+$/ } sub is_integer { $_[0] =~ /^[+-]?\d+$/ } sub is_float { $_[0] =~ /^[+-]?\d+\.?\d*$/ }` [download] Also, use \z if you wanted to "match the actual end of the string and not ignore an optional trailing newline" (perlre)	[reply] [d/l] [select]
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Re: Is Array Element Numeric? (was I wonder...) by fruiture (Curate) on Aug 22, 2002 at 12:52 UTC
It doesn't make a difference if it's an array element or a simple scalar, in any case the perlfaq has answered it. See `perldoc -q 'determine.*number'`. -- http://fruiture.de	[reply]
Re: Is Array Element Numeric? (was I wonder...) by smitz (Chaplain) on Aug 22, 2002 at 13:24 UTC
Like fruiture said, perdoc has the answer... #!perl -w # use strict; my @array = (100, 'a string!', 45.678, 0.43243, '', "", 0, "another no +rmal string with a carriage return \n"); foreach (@array) { if (/\D/) { print "$_ contains non-digits\n"; } elsif (/^\d+$/) { print "$_ is a whole number\n"; } elsif (/^-?\d+$/) { print "$_ is an integer\n"; } elsif (/^[+-]?\d+$/) { print "$_ is a +/- integer\n"; } elsif (/^-?\d+\.?\d$/) { print "$_ is a real number\n"; } elsif (/^-?(?:\d+(?:\.\d)?\|\.\d+)$/) { print "$_ is a decimal number\n"; } elsif (/^([+-]?)(?=\d\|\.\d)\d(\.\d)?([Ee]([+-]?\d+))?$/) { print "$_ is a C float\n"; } else { print "$_ not a number format I recognise, bud.\n"; } } [download] SMiTZ	[reply] [d/l]
Re: Is Array Element Numeric? (was I wonder...) by Bird (Pilgrim) on Aug 22, 2002 at 20:34 UTC
Personally, I'd put much more faith in theDamian and Abigail's code than my own. I'd use Regexp::Common. `use Regexp::Common qw /number/; for ('1', 'flip', '-2.3e14', '0.01', 'flop') { /$RE{num}{real}/ and print "Yup, $_ is a number!\n"; }` [download] -Bird	[reply] [d/l]
Re: Is Array Element Numeric? (was I wonder...) by moodster (Hermit) on Aug 22, 2002 at 12:58 UTC
Well, you could always perform some kind of numeric operation on your array element and see if performs as you'd expect. If it doesn't, it's probably a string. Try this for example: `if( abs( $array[ 0 ] ) != 0 ) { # the absolut value of this scalar is not 0, so it's probably not a + string }` [download] This works with floats as well as really large numbers (like "5.4e+10"), but beware: the absolute value of 0 is 0, so that's a false negative. I'll leave the handling of 0 as an excercise for the reader :) Cheers, --Moodster	[reply] [d/l]
Re: Is Array Element Numeric? (was I wonder...) by fglock (Vicar) on Aug 22, 2002 at 15:18 UTC
`if ($array[0] eq (0+$array[0])) { # certainly IS a number } else { # might be a "string" number: # might contain extra space, or plus sign, # or extra zeroes, ... # Add more checking here if you need. }` [download]	[reply] [d/l]