Sort hash by array

Question

I have a hash and an array with same length like the following:

h = {:a => 1, :b => 2, :c => 3, :d => 4}
a = [2, 0, 1, 0]

I want to order the hash in increasing order of the values in the array. So the output would be something like:

h = {:b => 2, :d => 4, :c=> 3, :a => 1}

Ideally I want to introduce some randomness for ties. For the previous example, I want either the previous output or:

h = {:d => 4, :b => 2, :c=> 3, :a => 1}

This is what I tried.

b = a.zip(h).sort.map(&:last)
p Hash[b]
# => {:b=>2, :d=>4, :c=>3, :a=>1}

But I am not sure how to introduce the randomness.

I am not getting your array's role to sort the hash... Explain more about ..increasing order of the values in the array. — Arup Rakshit
– Arup Rakshit, Commented Apr 5, 2015 at 14:32
Each (key, value) corresponds to an value of the array. For example :a => 1 corresponds to 2 as :b => 2 corresponds to 0. In the output hash the "zeros" should come first, the "ones" second etc. — igavriil
– igavriil, Commented Apr 5, 2015 at 14:36
When addressing a question that seeks clarification (e.g., @Arup's), it is generally better to edit your question (e.g., "Edit: ...), than to respond with comments, as some readers may not read all he comments. — Cary Swoveland
– Cary Swoveland, Commented Apr 5, 2015 at 16:31

steenslag · Accepted Answer · 2015-04-05 14:36:43Z

2

h.to_a.sort_by.each_with_index{|el,i| [a[i], rand]}.to_h

answered Apr 5, 2015 at 14:36

steenslag

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3 Comments

Cary Swoveland Over a year ago

I don't believe you need to_a.

steenslag Over a year ago

@CarySwoveland You are right. I stumbled upon it. Since I'm not in the habit of sorting hashes, I was mildly surprised sort_by returned an array. Considered an explicit to_a better, to explain the to_h,but not sure about it. Not very important though.

Cary Swoveland Over a year ago

A detail: Since Hash#each returns a two-element array, Enumerable#sort_by (and other Enumerable methods) acts on a hash the same way it acts on an array of two-element arrays.

Cary Swoveland · Accepted Answer · 2015-04-05 16:14:00Z

1

You could modify what you have slightly:

def doit(h,a)
   Hash[a.zip(h).sort_by { |e,_| [e,rand] }.map(&:last)]
end

doit(h,a) #=> { b=>2, d=>4, c=>3, a=>1 }
doit(h,a) #=> { d=>4, b=>2, c=>3, a=>1 }
doit(h,a) #=> { b=>2, d=>4, c=>3, a=>1 }
doit(h,a) #=> { b=>2, d=>4, c=>3, a=>1 }

answered Apr 5, 2015 at 16:14

Cary Swoveland

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