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module CoreExtensions
module Array
def collapse
self.inject([]) do |a, v|
if existing = a.find {|o| o.eql?(v)}
yield(existing, v)
else
a << v
end
a
end
end
end
end
Array.send(:include, CoreExtensions::Array)
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Kind of handy for reporting, where you need to collapse line items into a summary. This example may make it clear:
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class Item < Struct.new(:code, :quantity)
def eql?(b)
code == b.code
end
alias_method :==, :eql?
def hash
code.hash
end
def to_s
"#{code} - #{quantity}"
end
end
summary = [Item.new("a", 1), Item.new("a", 2), Item.new("b", 5)].collapse {|a, b| a.quantity += b.quantity}
summary.collect(&:to_s) # => ["a - 3", "b - 5"]
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