### Re: How to avoid an alphabet and integer next to it in a string?

by kcott (Bishop)
 on Mar 21, 2014 at 20:01 UTC ( #1079348=note: print w/replies, xml ) Need Help??

G'day piscean,

Welcome to the monastery.

You can do that like this. The tests include one- and two-letter symbols with and without numbers. I'll leave you to replace my rough atomic weights with more precise ones.

```#!/usr/bin/env perl -l

use strict;
use warnings;

my %weight = (C => 12, O => 16, Cl => 35.5);

my %tests = (
phenol => ['C6H5OH', 6 * 12 + 1 * 16],
chloroform => ['CHCl3', 1 * 12 + 3 * 35.5],
);

for my \$compound (keys %tests) {
print '-' x 40;
print "Compound:   \$compound";
my \$formula = \$tests{\$compound}[0];
print "Formula:    \$formula";
my \$calculated = 0;
\$formula =~ s{([A-Z][a-z]?)(\d*)}{
exists \$weight{\$1} and \$calculated += \$weight{\$1} * (\$2 || 1)
}eg;
print "Expected:   \$tests{\$compound}[1]";
print "Calculated: \$calculated";
}

Output:

```----------------------------------------
Compound:   phenol
Formula:    C6H5OH
Expected:   88
Calculated: 88
----------------------------------------
Compound:   chloroform
Formula:    CHCl3
Expected:   118.5
Calculated: 118.5

-- Ken

Replies are listed 'Best First'.
Re^2: How to avoid an alphabet and integer next to it in a string?
by piscean (Acolyte) on Mar 21, 2014 at 20:46 UTC
Thanks Ken! It was really helpful :) I've used Chemistry::MolecularMass module to have precise atomic weights.

I haven't used Chemistry::MolecularMass previously (in fact, I wasn't aware of its existence until now); however, looking at its documentation, it would appear another (completely untested) solution would be:

```use Chemistry::MolecularMass;
my \$mm = Chemistry::MolecularMass::->new();
\$mm->replace_elements(H => 0);
my \$no_H_mass = \$mm->calc_mass(\$your_formula);

-- Ken

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