Create a Hash from two arrays of different sizes and iterate until none of the keys are empty

Question

Having two arrays of different sizes, I'd like to get the longer array as keys and the shorter one as values. However, I don't want any keys to remain empty, so that is why I need to keep iterating on the shorter array until all keys have a value.

EDIT: I want to keep array longer intact, but without empty values, that means keep iterating on shorter until all keys have a value.

longer  = [1, 2, 3, 4, 5, 6, 7]
shorter = ['a', 'b', 'c']

Hash[longer.zip(shorter)]
#=> {1=>"a", 2=>"b", 3=>"c", 4=>nil, 5=>nil, 6=>nil, 7=>nil}

Expected Result

#=> {1=>"a", 2=>"b", 3=>"c", 4=>"a", 5=>"b", 6=>"c", 7=>"a"}

`longer.each_with_object({}).with_index { |(x,hsh),i| hsh[x] = shorter[i % shorter.size] } #=> {1=>"a", 2=>"b", 3=>"c", 4=>"a", 5=>"b", 6=>"c", 7=>"a"} ` — bjhaid, Oct 20 '16 at 14:23

score 7 · Accepted Answer · answered Oct 20 '16 at 14:24

7

Here's an elegant one. You can "loop" the short array

longer  = [1, 2, 3, 4, 5, 6, 7]
shorter = ['a', 'b', 'c']

longer.zip(shorter.cycle).to_h # => {1=>"a", 2=>"b", 3=>"c", 4=>"a", 5=>"b", 6=>"c", 7=>"a"}

answered Oct 20 '16 at 14:24

Sergio Tulentsev

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@AndreyDeineko: lots of stackoverflowing :) – Sergio Tulentsev Oct 20 '16 at 14:26
Neat !! Didn't know about cycle at all :O – Sam Oct 20 '16 at 14:27
I am seeing all these answers and realizing, that i'd also start thinking of some `each_with_object`/`inject` stuff.. meeh learn learn and learn again – Andrey Deineko Oct 20 '16 at 14:28
2

@AndreyDeineko: `each_with_object` is my go-to tool. it's the swiss army knife of enumerable processing :) – Sergio Tulentsev Oct 20 '16 at 14:29
The de-facto official Ruby documentation unfortunately does not show methods from included modules, so the gems in [`Enumerable`](http://ruby-doc.org/core/Enumerable.html) are often overlooked when working with arrays. Same for `Numeric < Integer < Fixnum`. – Stefan Oct 20 '16 at 14:34
@Stefan: well yes, that is logical behavior. It does list Enumerable in "included modules", though. – Sergio Tulentsev Oct 20 '16 at 14:37
Flawless Victory !. Thank you Serio. – Leo Oct 20 '16 at 14:40
@SergioTulentsev the documentation generated by YARD is much better in that regard: http://www.rubydoc.info/stdlib/core/Array – Stefan Oct 20 '16 at 14:48
@Stefan: indeed, it is! I wonder, is it a special case for Array or do they flatten included modules for all classes? – Sergio Tulentsev Oct 20 '16 at 14:59
@SergioTulentsev it seem to be an [RDoc limitation](http://stackoverflow.com/q/1651959/477037). – Stefan Oct 20 '16 at 15:07
Sergio, you don't need to say, "Here's an elegant one". Everybody knows all your answers are elegant. – Cary Swoveland Oct 20 '16 at 15:46
1

@CarySwoveland: oh, stop it, you :) – Sergio Tulentsev Oct 20 '16 at 15:51

score 1 · Answer 2 · answered Oct 20 '16 at 14:18

1

A crude way until you find something more elegant: Slice the longer array as per length of shorter one, and iterate over it to re-map the values.

mapped = longer.each_slice(shorter.length).to_a.map do |slice|
           Hash[slice.zip(shorter)]
         end
=> [{1=>"a", 2=>"b", 3=>"c"}, {4=>"a", 5=>"b", 6=>"c"}, {7=>"a"}]

Merge all hashes withing the mapped array into a single hash

final = mapped.reduce Hash.new, :merge
=> {1=>"a", 2=>"b", 3=>"c", 4=>"a", 5=>"b", 6=>"c", 7=>"a"}

answered Oct 20 '16 at 14:18

Sam

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15

Well, I'll just leave this here for an alternate (longer) approach. Sergio's answer is the best way to achieve this though. – Sam Oct 20 '16 at 14:30
1

You were at least the first to understand the OP's intentions. – Sagar Pandya Oct 20 '16 at 14:36
@sagarpandya82 ;) Thanks for noticing that – Sam Oct 21 '16 at 10:48

Cary Swoveland · Answer 3 · 2016-10-21T04:45:21.463

Here's a fun answer.

longer  = [1, 2, 3, 4, 5, 6, 7]
shorter = ['a', 'b', 'c']

h = Hash.new do |h,k|
  idx = longer.index(k)
  idx ? shorter[idx % shorter.size] : nil
end
  #=> {}

h[1] #=> a
h[2] #=> b
h[3] #=> c
h[4] #=> a
h[5] #=> b
h[6] #=> c
h[7] #=> a
h[8] #=> nil

h #=> {}

h.values_at(3,5) #=> ["c", "b"]

If this is not good enough (e.g., if you wish to use Hash methods such as keys, key?, merge, to_a and so on), you could create the associated hash quite easily:

longer.each { |n| h[n] = h[n] }
h #=> {1=>"a", 2=>"b", 3=>"c", 4=>"a", 5=>"b", 6=>"c", 7=>"a"}

Create a Hash from two arrays of different sizes and iterate until none of the keys are empty

3 Answers3