1

I have a hash which is named h. I want to store the contents in a multidimensional array named ar. I am getting the error no implicit conversion from nil to integer.

Here is my code:

h = {"bob" => {email: "abc" , tel: "123"} , "daisy" => {email: "cab" , tel: "123456"}}

keys = h.keys

l = h.length 

ar = Array.new(l) { Array.new(3) }

for i in 0..l-1
  ar[[2][i]] = keys[i]
  ar[[1][i]] = h[keys[i]][:email]
  ar[[0][i]] = h[keys[i]][:tel]
end

puts ar.to_s

The desired output is: 

[[email_1, email_2, ..][tel_1, tel_2, ..][name_1, name_2, ..]]

For example:

[["abc", "cab"] , ["123", "123456"] , ["bob", "daisy"]]
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4 Answers 4

Reset to default
2

This is the way I would handle this: 

h.values.each_with_object({}) do |h,obj|
  obj.merge!(h) { |_k,v1,v2| ([v1] << v2).flatten }
end.values << h.keys
#=> [["abc", "cab"], ["123", "123456"], ["bob", "daisy"]]
  • First grab all the values (as Hashes)
  • loop through them with an accumulator ({})
  • merge! the values into the accumulator and on conflict append them to an array
  • return the values from the accumulator
  • then append the original keys

This is less explicit than @mudasobwa's answer and relies on the order of the first value to determine the output. e.g. if :tel came before :email the first 2 elements would have a reversed order

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2 Comments

Your code works. Can you please suggest a way to improve mine or tell me where i am going wrong
@AkshatBansal let's start with what you think ar[[2][0]] represents because it actually means ar[2] because you are creating an Array ([2]) and then calling Array#[] on it thus [2][0] #=> 2 the problem here is that [2][1] #=> nil so ar[[2][1]] is equivalent to ar[nil] which raises the error on the second iteration. what you meant was ar[2][0] and ar[2][1] but that also has a mistake as ar = [[nil,nil,nil],[nil,nil,nil]] (notice no ar[2] only ar[0] and ar[1].
2

[2][i] returns nil for i > 0. ar[nil] raises the exception.

Here is what you do:

arr = h.map { |k, v| [v[:email], v[:tel], k] }.reduce(&:zip)

To make your code work:

Change

ar = Array.new(l) { Array.new(3) }

To

ar = Array.new(3) { Array.new(l) }

Change

ar[[2][i]] = keys[i]
ar[[1][i]] = h[keys[i]][:email]
ar[[0][i]] = h[keys[i]][:tel]

To

ar[2][i] = keys[i]
ar[1][i] = h[keys[i]][:email]
ar[0][i] = h[keys[i]][:tel]
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3 Comments

Sorry i did not got your point , can you please tell what should i do to correct it
It is not giving error but also not giving the output needed.
+1 for explaining the problem with the OPs solution but please note your proposed solution only works with 2 keys in the main hash otherwise the output gains increasing depth
1

What you mostly should do is to stop writing PHP code with Ruby syntax. Here it’s how is to be done in Ruby:

h.map { |k, v| [v[:email], v[:tel], k] }.reduce(&:zip)

or, even better, if you are certain of elements order in nested hashes:

h.map { |k, v| [*v.values, k] }.reduce(&:zip).map(&:flatten)

All the methods map, reduce and zip are thoroughly described in the documentation.

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8 Comments

Your "even better" relies on the need for the elements to be in the same order where as your first example (which is better) does not
@engineersmnky ...which is precisely described in the comment to “even better,” isn’t it?
describing a caveat does not make a solution "better" though does it? What makes it better? less key strokes?
@engineersmnky indeed, I am always forgetting who does flatten the result and who does not. It would work for any amount of keys with .map(&:flatten) afterwards.
@engineersmnky always welcome; The former one is likely the exact solution for the input given. The latter is the generalized. :)
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0 
h.map { |k, v| [*v.values_at(:email, :tel), k] }.transpose
  #=> [["abc", "cab"], ["123", "123456"], ["bob", "daisy"]]

The intermediate calculation is as follows.

h.map { |k, v| [*v.values_at(:email, :tel), k] }
  #=> [["abc", "123", "bob"], ["cab", "123456", "daisy"]]
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