CODEWITHSUNDEEP
rubyarrays
cjhin
cjhin

Reputation: 235

Ruby group by range, array of numbers?

I'm trying to create a histogram from an array of numbers in the range [0,1].

Is there a way to use group_by to separate the array into N groups/bins by numeric interval (or some other fun Ruby one-liner)?

This is my current, boring, solution:

# values == array containing floating point numbers in the range [0,1]

n = 10

# EDITED from Array.new(n, 0) to Array.new(n, []), thanks emaillenin!
histogram = Array.new(n, [])
values.each do |val|
  histogram[(val * n).ceil - 1].push(val)
end

Upvotes: 1

Views: 1637

Answers (2)

Cary Swoveland
Cary Swoveland

Reputation: 110675

This is one way to do it.

Code

def freq_by_bin(nbr_bins, *values)
  nbr_bins.times.to_a.product([0]).to_h.tap { |h|
    values.each { |v| h.update({ (v*nbr_bins).to_i=>1 }) { |_,o,_| o+1 } } }
end

Example

values =  [0.30, 0.25, 0.63, 0.94, 0.08, 0.94, 0.01,
           0.41, 0.28, 0.69, 0.61, 0.12, 0.66]
freq_by_bin(10, *values)
  #=> {0=>2, 1=>1, 2=>2, 3=>1, 4=>1,
  #    5=>0, 6=>4, 7=>0, 8=>0, 9=>2}

def histogram(nbr_bins, *values)
  h = freq_by_bin(nbr_bins, *values)
  puts "\nfreq"
  h.values.max.downto(0) do |n|
    print "%2d|" % n
    puts nbr_bins.times.with_object('   ') { |i,row|
           row << ((h[i]==n) ? ' X ' : '   ') }
  end
  puts "   __"+"___"*nbr_bins
  puts nbr_bins.times.each_with_object('      ') { |i,row| row << "%2d " % i }
end

histogram(10, *values)

freq
 4|                      X          
 3|                                 
 2|    X     X                    X 
 1|       X     X  X                
 0|                   X     X  X    
   ________________________________
       0  1  2  3  4  5  6  7  8  9

Notes

  • There are several ways to construct the hash whose elements are bin=>freq. Using Enumerable#group_by, which you mentioned and @diego used is one. I've used the form of Hash#update (aka Hash#merge!) that takes a block.

  • I used Object#tap merely to avoid the need to create a temporary (non-block) variable for the initialized hash.

Upvotes: 1

DiegoSalazar
DiegoSalazar

Reputation: 13521

Not sure what you're trying to do but maybe this helps?

values = [0.0, 0.1, 0.2, 0.3]
values.group_by { |v| (v * 10).ceil - 1 }

That returns a hash:

{-1=>[0.0], 0=>[0.1], 1=>[0.2], 2=>[0.3]}

Upvotes: 3

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