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### Re^3: The Definitive Unit Conversion Script

by Aristotle (Chancellor)
 on Dec 13, 2002 at 19:37 UTC ( #219716=note: print w/replies, xml ) Need Help??

"Definitive" in the sense that it effortlessly converts into all related units, not in the amount of units handled. :)

Of course it would be nice to add some limited parsing and intrinsic "understanding" of units and I can see how I'd go about implementing the basic idea (split into numerator and denominator, convert, divide), but how complex a unit specification should it be able to handle? I don't want to add so much weight that it turns into a small expression evaluator. I'm thinking one unit in the numerator, one in the denominator, and one power given for each sounds like a viably complex, sufficiently flexible spec.

Makeshifts last the longest.

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(tye)Re3: The Definitive Unit Conversion Script
by tye (Sage) on Dec 13, 2002 at 20:20 UTC

This doesn't have to be complicated. Split on * and before /, then check for /\^\d+\$/:

my @units= split m#(?<=.)(?:(?=/)|\*)#, \$units, -1; my %power; for my \$unit ( @units ) { my \$power= 1; if( \$unit =~ s#\^(\d+)\$## ) { \$power= \$1; } if( \$unit =~ s#^/## ) { \$power= -\$power; } \$power{\$unit} += \$power; } # ...
then you have to find units that you can convert to with matching powers. So, if you start with kg/cm/sec [ which becomes (kg=>1,cm=>-1,sec=>-1) ] and are asked to return lb/ft/hr (lb=>1,ft=>-1,hr=>-1), then you have to convert from kg to lb, then convert cm to either ft or hr (there will be no cm-to-hr path so you'll do cm-to-ft), then convert the left-overs, sec-to-hr. And you're done.

(Updated and tested.)

- tye

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