I have a array of hashes which key are Date
and value are Integer
.
This is a test code to emulate it.
hashes = 2000.times.map do |i|
[Date.new(2017) - i.days, rand(100)]
end.to_h
I want to get values of a specific period.
At first I wrote with Range#include?
, but it was quite slow.
Benchmark.measure do
hashes.select{|k,v| (Date.new(2012,3,3)..Date.new(2012,6,10)).include?(k)}
end
#<Benchmark::Tms:0x007fd16479bed0 @label="", @real=2.9242447479628026, @cstime=0.0, @cutime=0.0, @stime=0.0, @utime=2.920000000000016, @total=2.920000000000016>
With simple greater or less than operator it became 60 times faster.
Benchmark.measure do
hashes.select{|k,v| k >= Date.new(2012,3,3) && k <= Date.new(2012,6,10)}
end
#<Benchmark::Tms:0x007fd162b61670 @label="", @real=0.05436371313408017, @cstime=0.0, @cutime=0.0, @stime=0.0, @utime=0.05000000000001137, @total=0.05000000000001137>
I thought these two expression are basically same.
Why there is so big difference?
You need to use Range#cover? instead of Range#include?, and to calculate the range just once, not once for each element of measure
. cover?
compares the block variable k
with the end-points of the range; include?
(for non-numeric objects, such as dates) compares each element in the range with the block variable until it finds a match or concludes there is no match (similar to Array#include?).
In addition, you wish to consider the first and only key of each element of hashes
(a hash), so if that hash is h
, the first key-value pair is h.first
, and the key of that pair is h.first.first
.
require 'date'
Benchmark.measure do
r = Date.new(2012,3,3)..Date.new(2012,6,10)
hashes.select{|h| r.cover? h.first.first }
end
This should be nearly identical to your second method in terms of execution speed.
An example
hashes = [{ Date.new(2012,3,1)=>1 }, { Date.new(2012,4,20)=>2 },
{ Date.new(2012,6,10)=>3 }, { Date.new(2012,6,11)=>4 }]
#=> [{#<Date: 2012-03-01 ((2455988j,0s,0n),+0s,2299161j)>=>1},
# {#<Date: 2012-04-20 ((2456038j,0s,0n),+0s,2299161j)>=>2},
# {#<Date: 2012-06-10 ((2456089j,0s,0n),+0s,2299161j)>=>3},
# {#<Date: 2012-06-11 ((2456090j,0s,0n),+0s,2299161j)>=>4}]
r = Date.new(2012,3,3)..Date.new(2012,6,10)
hashes.select{|h| r.cover? h.first.first }
#=> {#<Date: 2012-04-20 ((2456038j,0s,0n),+0s,2299161j)>=>2,
# #<Date: 2012-06-10 ((2456089j,0s,0n),+0s,2299161j)>=>3}