in reply to Re: Re: Regexps for Parsing Brackets in Chemical Formulae
in thread Regexps for Parsing Brackets in Chemical Formulae

You were close. That should do it:
use strict;
my %count;

# added gratuitous parentheses for embedded formula testing sake.
$_='Mo(P(H)3)4(CO)(NH2C2(H)5)';


# at each iteration do subformula with rigtmost left parenthesis. 
# quit when no more parenthesis
s/(.*)\((.*?)\)(\d*)/$1 . $2 x ($3 ? $3 : 1) /e while m/\(/;

s/([A-Z](?:[a-z])?)(\d*)/  $count{$1} += $2 ? $2  : 1 ;''/eg;

printf "%-2s %3d\n", $_, $count{$_} for sort keys %count;

[download]
It prints: 
C    3
H   19
Mo   1
N    1
O    1
P    4

[download]

-- stefp

Replies are listed 'Best First'.
Re: Re: Re: Re: Regexps for Parsing Brackets in Chemical Formulae
by Elgon (Curate) on Nov 05, 2001 at 09:26 UTC

    Stefp,

    Muchas gracias - one minor alteration to take account of the fact that certain artificial elements have, under certain nomenclatures, three letters rather than one or two...

    s/([A-Z](?:[a-z]{0,2})?)(\d*)/  $count{$1} += $2 ? $2  : 1 ;''/eg;

    Otherwise, perfect!

    Ta, Elgon.

    "Without evil there can be no good, so it must be good to be evil sometimes.
    --Satan, South Park: Bigger, Longer, Uncut.

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[d/l]
      Not quite perfect:

         s/([A-Z][a-z]{0,2})(\d*)/ $count{$1} += $2 ? $2 : 1 '' /eg;

      is cleaner. The (?:) was a unneeded left-off in my code and when you added the {0,2} modifier, the ? modifier became redundant. Or {2}? could be used instead of {0,2}.

      Strangely for the golfers {,2} is not supported; it should be expected to be supported because {2,} is.

      -- stefp

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