Sha256: faf4354e2d8afb5ded8d205ee24ee118a5b7eb412a0b711f7aab4a3a8d4f7171
Contents?: true
Size: 1.73 KB
Versions: 9
Compression:
Stored size: 1.73 KB
Contents
class Hash
# Like group_by, but allows hash values to be grouped with weeding out the keys.
#
# Example:
#
# birthdays = {...} # Maps each person to his/her birthday.
#
# Now I want to have the list of people that have their birthday
# on a specific date. This can be done by creating a hash first,
# using group_by:
#
# birthdays.group_by{|person, birthday| birthday}
#
# This returns:
#
# {date=>[[person1, date], [person2, date], [person3, date]]}
#
# ... which is a bit inconvient. Too many dates. I would rather
# like to have:
#
# {date=>[person1, person2, person3]]}
#
# This can be achieved by:
#
# birthdays.inject!({}){|h, (person, date)| (h[date] ||= []) << person}
#
# I've used this pattern just once too often, so I moved the code
# to Hash (and Enumerable, for associative arrays). Here's the
# cleaner code:
#
# birthdays.group_by_value
#
# h = {"A"=>1, "B"=>1, "C"=>1, "D"=>2, "E"=>2, "F"=>2, "G"=>3, "H"=>3, "I"=>3}
#
# h.group_by{|k, v| v} # ==> {1=>[["A", 1], ["B", 1], ["C", 1]], 2=>[["D", 2], ["E", 2], ["F", 2]], 3=>[["G", 3], ["H", 3], ["I", 3]]}
# h.group_by_value # ==> {1=>["A", "B", "C"], 2=>["D", "E", "F"], 3=>["G", "H", "I"]}
# h.sort.group_by_value # ==> [[1, ["A", "B", "C"]], [2, ["D", "E", "F"]], [3, ["G", "H", "I"]]]
#
# CREDIT: Erik Veenstra
def group_by_value
res = {}
each{|k, v| (res[v] ||= []) << k}
res
end
end
# Not sure this is a good idea for enumerable.
#
#module Enumerable
#
# # For associative arrays, like the result of Hash#sort.
# #
# def group_by_value
# kv = k = v = nil
# res = []
# each{|k, v| (res.assoc(v) || (res << kv=[v, []]; kv)).last << k}
# res
# end
#
#end
Version data entries
9 entries across 9 versions & 1 rubygems