Ruby code hash of array based of a cutoff

Question

I have an array of floating numbers and a certain cutoff:

myData = [1.3,1.5,1.7,1.7,16.7,18.4,19.2,19.5,19.6,20.2,20.8,58.4,60.7,
          61.2,61.2,116.4,121.2,122.7,123.2,123.2,138.5,149.5,149.5]
myBin = 5.3

I'd like to build a hash of arrays so that the difference by subtraction between the last element and the first element of the array is less or equal to myBin (5.3)

myHash = {
'hap_1' => [1.3,1.5,1.7],
'hap_2' => [16.8, 18.4,19.2,19.5,19.6,20.2,20.8],
'hap_3' => [58.4,60.7,61.2,61.2],
'hap_4' => [116.4,121.2],
'hap_5' => [122.7,123.2,123.2],
'hap_6' => [138.5],
'hap_7' => [149.5,149.5]}

Thank you so much in advance for your time and helpful assistance. Cheers

Have you attempted a solution yourself?

Sagar Pandya
– Sagar Pandya

2017-10-26 18:03:53 +00:00
Commented Oct 26, 2017 at 18:03 — Sagar Pandya
– Sagar Pandya, Commented Oct 26, 2017 at 18:03
You should use snake_case for variable names in Ruby.

Stefan
– Stefan

2017-10-26 18:29:30 +00:00
Commented Oct 26, 2017 at 18:29 — Stefan
– Stefan, Commented Oct 26, 2017 at 18:29

Ilya · Accepted Answer · 2017-10-26 18:16:52Z

6

Enumerable#slice_before can solve your problem:

first = myData[0]
myData.slice_before { |e| first = e if e - first > myBin }.to_a
#=> [[1.3, 1.5, 1.7, 1.7],
#    [16.7, 18.4, 19.2, 19.5, 19.6, 20.2, 20.8],
#    [58.4, 60.7, 61.2, 61.2],
#    [116.4, 121.2],
#    [122.7, 123.2, 123.2],
#    [138.5],
#    [149.5, 149.5]]

answered Oct 26, 2017 at 18:16

Ilya

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2 Comments

Sagar Pandya Over a year ago

Solves the core issue however note the OP wanted a hash. Unless you left it on purpose to leave the OP something to do:)

Cary Swoveland Over a year ago

Lovely answer. As you are relying on nil being returned when the if clause is not true, it may be more clear to write myData.slice_before { |n| n-first > myBin ? (first=n) : false }.to_a. Two variants are myData.slice_when { |_,n| n-first > myBin ? (first=n) : false }.to_a and myData.chunk_while { |_,n| n-first <= myBin ? true : !(first=n) }.to_a.

Cary Swoveland · Accepted Answer · 2017-10-26 19:39:27Z

1

myData.drop(1).each_with_object([[myData.first]]) { |n,a|
  n - a.last.first <= myBin ? (a.last << n) : a << [n] }.
  each.with_index(1).with_object({}) { |(a,i),h| h["hap_#{i}"] = a }
  #=> {"hap_1"=>[1.3, 1.5, 1.7, 1.7],
  #    "hap_2"=>[16.7, 18.4, 19.2, 19.5, 19.6, 20.2, 20.8],
  #    "hap_3"=>[58.4, 60.7, 61.2, 61.2],
  #    "hap_4"=>[116.4, 121.2],
  #    "hap_5"=>[122.7, 123.2, 123.2],
  #    "hap_6"=>[138.5],
  #    "hap_7"=>[149.5, 149.5]}

edited Oct 26, 2017 at 19:39

answered Oct 26, 2017 at 18:33

Cary Swoveland

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Comments

Stefan · Accepted Answer · 2017-10-27 09:02:54Z

You could build a customer enumerator that works like chunk_while, but compares each chunk's first element to the current one, i.e. 1.3 to 1.5, then 1.3 to 1.7 and so on:

module Enumerable
  def chunk_while1
    return enum_for(__method__) unless block_given?
    each_with_object([]) do |elt, result|
      if result.last && yield(result.last.first, elt)
        result.last << elt
      else
        result << [elt]
      end
    end
  end
end

Usage:

data = [
  1.3, 1.5, 1.7, 1.7, 16.7, 18.4, 19.2, 19.5, 19.6, 20.2, 20.8, 58.4, 60.7,
  61.2, 61.2, 116.4, 121.2, 122.7, 123.2, 123.2, 138.5, 149.5, 149.5
]

result = data.chunk_while1 { |i, j| j - i <= 5.3 }
#=> [
#     [1.3, 1.5, 1.7, 1.7],
#     [16.7, 18.4, 19.2, 19.5, 19.6, 20.2, 20.8],
#     [58.4, 60.7, 61.2, 61.2],
#     [116.4, 121.2],
#     [122.7, 123.2, 123.2],
#     [138.5],
#     [149.5, 149.5]
#   ]

The result can then be converted to a hash, e.g. via:

result.map.with_index(1) { |a, i| ["hap_#{i}", a] }.to_h
#=> {
#     "hap_1"=>[1.3, 1.5, 1.7, 1.7],
#     "hap_2"=>[16.7, 18.4, 19.2, 19.5, 19.6, 20.2, 20.8],
#     "hap_3"=>[58.4, 60.7, 61.2, 61.2],
#     "hap_4"=>[116.4, 121.2],
#     "hap_5"=>[122.7, 123.2, 123.2],
#     "hap_6"=>[138.5],
#     "hap_7"=>[149.5, 149.5]
#   }

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