Mapping two dimensional array to one dimensional array with indexes

Question

I have 2d array like this:

ary = [
  ["Source", "attribute1", "attribute2"],
  ["db", "usage", "value"],
  ["import", "usage", "value"],
  ["webservice", "usage", "value"]
]

I want to pull out the following in hash:

{1 => "db", 2 => "import", 3 => "webservice"} // keys are indexes or outer 2d array

I know how to get this by looping trough 2d array. But since I'm learning ruby I thought I could do it with something like this

ary.each_with_index.map {|element, index| {index => element[0]}}.reduce(:merge)

This gives me :

{0=> "Source", 1 => "db", 2 => "import", 3 => "webservice"}

How do I get rid of 0 element from my output map?

tokland · Accepted Answer · 2013-03-20 16:10:17Z

1

I'd write:

Hash[ary.drop(1).map.with_index(1) { |xs, idx| [idx, xs.first] }]
#=> {1=>"db", 2=>"import", 3=>"webservice"}

answered Mar 20, 2013 at 16:10

tokland

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Comments

dbenhur · Accepted Answer · 2013-03-20 16:15:01Z

0

ary.drop(1) drops the first element, returns the rest.

You could build the hash directly without the merge reduction using each_with_object

ary.drop(1)
  .each_with_object({})
  .with_index(1) { |((source,_,_),memo),i| memo[i] = source }

Or map to tuples and send to the Hash[] constructor.

Hash[ ary.drop(1).map.with_index(1) { |(s,_,_),i| [i, s] } ]

answered Mar 20, 2013 at 15:58

dbenhur

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