Transform an array of hashes to an array of nested hashes

Question

I want to modify my array of hashes to facilitate better search performance

I have:

a = [ {"id" => 1, "name" => "Matt", "email" => "[email protected]"}, {"id" => 2, "name" => "Charlie", "email" => "[email protected]"} ]

I want to transform this into:

b = [ {1 => { "name" => "Matt", "email" => "[email protected]"}},{2 => { "name" => "Charlie", "email" => "[email protected]"}} ]

Note that the "id" field won't necessarily be a sequential or contiguous set, but each occurrence will be unique. Also, the hash nested as a value in b can contain 'id' key/value pair if that makes things easier.

Nate Murray · Accepted Answer · 2012-11-28 00:52:56Z

2

Try:

a.map{|record| the_id = record.delete("id"); {the_id => record}}

answered Nov 28, 2012 at 0:52

Nate Murray

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3 Comments

Amadan Over a year ago

This will create an array of 1-element hashes of hash-objects, not a hash of hash-objects as the OP wishes (i.e. it will just wrap each individual hash-object into its own private little hash).

kmkaplan Over a year ago

This will modify the content of the original a array

kmkaplan Over a year ago

@Amadan Matt does ask for an array of hashes… Although he is probably confused.

kmkaplan · Accepted Answer · 2012-11-28 01:09:59Z

2

To get the array you describe:

b = a.map {|i| { i["id"] => i } }

But note that if you are doing this to perform efficient searches by id then build a hash instead of an array:

b = a.inject({}) {|h,i| h[i["id"]]=i; h}

edited Nov 28, 2012 at 1:09

answered Nov 28, 2012 at 0:50

kmkaplan

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2 Comments

kmkaplan Over a year ago

@Matt Did you make sure you ran this in a fresh Ruby? Amadan’s first answer as well as Nate Murray’s will trash your a array so that my answer does not work anymore.

Matt Over a year ago

My apologies, I did indeed.

Amadan · Accepted Answer · 2012-11-28 01:15:17Z

1

a.each_with_object({}) { |x, h| h[x.delete('id')] = x }

This will construct a new hash ({}), pass it into the block as h with each element x. In the block x.delete('id') removes the id key/value from x, and returns it so it can be used as the index to assign a value to the resultant h hash.

EDIT per kmkaplan's comment: If you still need the original array, use this:

a.each_with_object({}) { |x, h| c = x.clone; h[c.delete('id')] = c }

EDIT per kmkaplan's other comment: If the OP really isn't confused, Nate Murray's answer is the right one.

edited Nov 28, 2012 at 1:15

answered Nov 28, 2012 at 0:45

Amadan

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1 Comment

kmkaplan Over a year ago

This will modify the content of the original a array.

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