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Sorting an Array by Frequency of Appearance
CodeExpectedActual
module Enumerable
def sort_by_frequency
histogram = inject(Hash.new(0)) { |hash, x| hash[x] += 1; hash}
sort_by { |x| [histogram[x], x] }
end
end
[1,2,3,4,1,2,4,8,1,4,9,16].sort_by_frequency
[3, 8, 9, 16, 2, 2, 1, 1, 1, 4, 4, 4] [3, 8, 9, 16, 2, 2, 1, 1, 1, 4, 4, 4]
[1,2] <=> [0,2]
1 1
[1,2] <=> [1,2]
0 0
[1,2] <=> [2,2]
-1 -1
[1,2] <=> [1,1]
1 1
[1,2] <=> [1,3]
-1 -1
[1,2] <=> [1]
1 1
[1,2] <=> [3]
-1 -1
[1,2] <=> [0,1,2]
1 1
[1,2] <=> []
1 1
module Enumerable
def sort_by_frequency_faster
histogram = inject(Hash.new(0)) { |hash, x| hash[x] += 1; hash}
sort_by { |x| histogram[x] }
end
end
[1,2,3,4,1,2,4,8,1,4,9,16].sort_by_frequency_faster
[16, 8, 3, 9, 2, 2, 4, 1, 1, 4, 4, 1] [16, 8, 3, 9, 2, 2, 4, 1, 1, 4, 4, 1]
module Enumerable
def sort_by_frequency_descending
histogram = inject(Hash.new(0)) { |hash, x| hash[x] += 1; hash}
sort_by { |x| [histogram[x] * -1, x]}
end
end
[1,2,3,4,1,2,4,8,1,4,9,16].sort_by_frequency_descending
[1, 1, 1, 4, 4, 4, 2, 2, 3, 8, 9, 16] [1, 1, 1, 4, 4, 4, 2, 2, 3, 8, 9, 16]
module Enumerable
def sort_distinct_by_frequency
histogram = inject(Hash.new(0)) { |hash, x| hash[x] += 1; hash }
histogram.keys.sort_by { |x| [histogram[x], x] }
end
end
[1,2,3,4,1,2,4,8,1,4,9,16].sort_distinct_by_frequency
[3, 8, 9, 16, 2, 1, 4] [3, 8, 9, 16, 2, 1, 4]