From: Mathieu Bouchard <matju@...>
Date: 2001-03-19T02:00:43+09:00
Subject: [ruby-talk:12821] units of measure


This is something i wrote a month ago. I'm not doing anything with it for
now, so I post it in case someone wants to pick it up. It's a system so
that units of measure can be computed together (class Unit) and so that
numeric values can be attached units (class Quantity)

# Copyright 2001 by Mathieu Bouchard
# Licensed under the same terms as Ruby

class Unit
	attr_reader :table
	def initialize(h)
		@table = h.dup
		@table.delete_if {|x| x==0 }
	end
	def to_s
		t = @table.keys.sort {|a,b| @table[a] <=> @table[b] }
		t1,t2 = t.find_all {|x| @table[x] > 0 },
			t.find_all {|x| @table[x] < 0 }
		t1,t2=[t1,t2].map {|ti|
			ti.map {|x|
				y=@table[x].abs
				y==1? "#{x}" : "#{x}^#{y.abs}"
			}.join('.')
		}
		t1='1' if t1.length==0
		return t1 if t2.length==0
		[t1,t2].join '/'
	end
	def inspect; to_s; end
	def +(other)
		h = @table.dup
		other.table.each {|k,v| h[k]||=0; h[k]+=v }
		Unit.new h
	end
	def -@
		h = @table.dup
		h.each {|k,v| h[k]=-v }
		Unit.new h
	end
	def -(other); self+-other; end
end

class Quantity
	attr_reader :value
	attr_reader :unit
	def initialize(value,unit)
		@value = value
		@unit = unit
	end
	def +(other)
		self.unit == other.unit or raise TypeError
		Quantity.new(self.value + other.value, self.unit)
	end
	def -@; Quantity.new(-self.value, self.unit); end
	def *(other)
		Quantity.new(self.value * other.value,
			self.unit + other.unit)
	end
	def /(other)
		Quantity.new(self.value / other.value,
			self.unit - other.unit)
	end
	def to_s
		[value,unit].join " "
	end
	def inspect; to_s; end
end


$u = Unit.new 'm'=>1,'s'=>-2; p $u
$v = Unit.new 'kg'=>1,'m'=>1; p $v
$w = $u+$v; p $w
p -$w

#=> m/s^2
#=> m.kg
#=> kg.m^2/s^2
#=> s^2/m^2.kg

$a = Quantity.new 9.8, $u; p $a
$b = Quantity.new 8888, Unit.new('m'=>1); p $b
$c = $a*$b*Quantity.new(42, Unit.new 'kg'=>1); p $c
p ($a*$a/$c) # lol

#=> 9.8 m/s^2
#=> 8888 m
#=> 3658300.8 kg.m^2/s^2
#=> 2.625262526e-05 1/s^2.kg