Finding indexes of each element in a multidimensional array in ruby

Question

Eg

:a=[["hello", "world"], ["good", "lord"], ["hello", "lord"]]

I need to find and record the indexes of each word with respect to the super-array. i.e

hello => 0,2
world => 0
lord => 1,2.

here's my shot ,but its very amateurish and lengthy.

all_tokens=tokens.flatten
all_tokens.each do|keyword|                                                                                      
    tokens.each do|token_array|
        if token_array.include?keyword
            x << i
        end
        i=i+1
    end    
    y[k] = x.clone
    y=y.clear
end

Sorry.Please substitute "tokens" for "a". And "keyword" is just a looping variable. — Shreyas
– Shreyas, Commented Apr 8, 2010 at 2:42
And as flOOr mentioned, getting an array,rather a multi-dimensional array, as a result is the goal.But, once the hash is processed, and even this works ! — Shreyas
– Shreyas, Commented Apr 8, 2010 at 2:57

Marc-André Lafortune · Accepted Answer · 2010-04-07 16:18:12Z

4

Slight improvement (imho) on vava's solution:

tokens = [["hello", "world"], ["good", "lord"], ["hello", "lord"]]

tokens_hash = Hash.new{|h, k| h[k] = []}

tokens.each_with_index do |subarr, i|
  subarr.each do |word|
    tokens_hash[word] << i
  end
end

answered Apr 7, 2010 at 16:18

Marc-André Lafortune

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1 Comment

fl00r Over a year ago

I've suggested same solution :)

Tuomas Pelkonen · Accepted Answer · 2010-04-07 15:48:28Z

2

ret = []
a.each_with_index {|x, i| if x.include?(keyword) then ret << i end }

answered Apr 7, 2010 at 15:48

Tuomas Pelkonen

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3 Comments

Ju Nogueira Over a year ago

I suppose keyword can be "hello", "world", "good" and "lord".

Mladen Jablanović Over a year ago

So this is an update of the part of the code from the question? Wouldn't be useful to have quoted complete working snippet here then?

fl00r Over a year ago

generally it is not working solution. firstly keyword is not defined, secondly, even if we will define keyword ret will return array of numbers, not hash that is the goal

Mladen Jablanović · Accepted Answer · 2010-04-07 17:22:40Z

2

a.each_with_index.inject({}){|acc,(elem,i)|
  elem.each{|e|
    acc[e] ||= []
    acc[e] << i
  }
  acc
}
#=> {"hello"=>[0, 2], "world"=>[0], "good"=>[1], "lord"=>[1, 2]}

edited Apr 7, 2010 at 17:22

answered Apr 7, 2010 at 16:17

Mladen Jablanović

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2 Comments

fl00r Over a year ago

you can't use each_with_index without block

Mladen Jablanović Over a year ago

I can, in Ruby >= 1.8.7. It's returning Enumerator instance.

vava · Accepted Answer · 2010-04-07 15:57:07Z

1

tokens = [["hello", "world"], ["good", "lord"], ["hello", "lord"]]

tokens_hash = Hash.new([])

tokens.each_with_index do |subarr, i|
    subarr.each do |word|
        tokens_hash[word] = tokens_hash[word] + [i]
    end
end

p tokens_hash #=>{"good"=>[1], "world"=>[0], "lord"=>[1, 2], "hello"=>[0, 2]}

My solution will scan the whole structure just once.

answered Apr 7, 2010 at 15:57

vava

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Comments

Wayne Conrad · Accepted Answer · 2010-04-07 16:38:46Z

1

Just for grins, a functional solution:

#!/usr/bin/ruby1.8

a = [["hello", "world"], ["good", "lord"], ["hello", "lord"]]

b = a.flatten.uniq.inject({}) do |hash, word|
  hash.merge(word => a.each_with_index.collect do |list, i|
               list.index(word) && i
             end.compact)
end

p b    # => {"world"=>[0], "good"=>[1], "lord"=>[1, 2], "hello"=>[0, 2]}

answered Apr 7, 2010 at 16:38

Wayne Conrad

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Comments

fl00r · Accepted Answer · 2010-04-07 16:46:57Z

1

a=[["hello", "world"], ["good", "lord"], ["hello", "lord"]]
result = Hash.new{|k,v| k[v] = []}
a.each_with_index{|b,i| b.each{|c| result[c] << i} }
result
#=> {"good"=>[1], "world"=>[0], "lord"=>[1, 2], "hello"=>[0, 2]}

answered Apr 7, 2010 at 16:46

fl00r

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