I have an array:
[1,2,3,4,5,6,7,8,9,10]
and I need to count three separate things.
1) All values less than or equal to 6.
2) All values equal to 7 or 8.
3) All values greater than 8.
What is the best way to do this without counting individual values and adding them all together?
Use Enumerable#count with a block.
[1,2,3,4,5,6,7,8,9,10].count { |val| val <= 6 }
[1,2,3,4,5,6,7,8,9,10].count { |val| val == 7 || val == 8 }
[1,2,3,4,5,6,7,8,9,10].count { |val| val > 8 }
arr = [1,2,3,4,5,6,7,8,9,10]
arr.select {|e| e <= 6}.size
#=> 6
arr.select {|e| e == 7 || e == 8}.size
#=> 2
arr.select {|e| e > 8}.size
#=> 2
How about this:
>> hash = Hash.new(0)
>> arr = [1,2,3,4,5,6,7,8,9,10]
>> arr.each { |e| hash[(e-7.5).truncate<=>0]+=1 }
>> hash
=> {-1=>6, 0=>2, 1=>2}
Or even more succinct:
>> arr = [1,2,3,4,5,6,7,8,9,10]
>> arr.each_with_object(Hash.new(0)) { |e,h| h[(e-7.5).truncate<=>0]+=1 }
=> {-1=>6, 0=>2, 1=>2}
.values => [6,2,2]. You could also write the block as {|e,h| h[(e+1)/2-4<=>0]+=1}.
.values is undefined. If an array is required, we should probably use .values_at(-1,0,1) to make it explicit, or .values_at(*-1..1) if we were being clever :-)values_at.More interesting, imo, is to answer @Luigi's three questions with a single statement (containing no semicolons). Here are two ways to do it:
a = [1,2,3,4,5,6,7,8,9,10]
a.inject([0,0,0]) {|arr,i| [arr[0]+(i<7 ? 1:0), arr[1]+((i>6 and i<9) ? 1:0), arr[2]+(i>8 ? 1:0)]}
a.slice_before(7).to_a.map {|arr| arr.slice_before(9).to_a}.flatten(1).map(&:size)
# => [6, 2, 2]
Edit: another, inspired by @staafl's answer:
arr.group_by {|e| (e+1)/2-4<=>0}.values.map(&:size)
Can you suggest others?