This may be very simple, but I don't know all of Ruby's array functions.
If I have a given array like:
values = [["a", 1], ["b", 3], ["c", 7], ... etc ]
I would like two functions:
There must be an easy way?
Hash[values]["b"] # => 3
Hash[values.map(&:reverse)][3] # => "b"
My first question is: Does this have to be an array? Hash is designed for this and has key / value lookup built-in.
You can create a Hash from an array by doing:
hash = Hash[values]
Then use hash["a"] # => 1
For the reverse, do: hash.key(1) # => "a"
The first is easy to achieve, by converting your array to a Hash with:
value_hash = Hash[values]
And access this with:
value_hash['b'] # => 3
For the other way around I would first like to know if you are sure that is is a unique request? So are both 'a','b','c',... and 1,3,7... etc. unique?
hash = array.to_h => Converts your array to a hash
hash[key] = value => Get the value associated with the key
hash.invert[key] = value => This method inverts your hash and you can select values
Yeah a hash is the answer, if you don't have duplicate keys of course. Otherwise you can use Array#assoc#rassoc which searches an array of arrays matching the first and last elements respectively:
ary = [["A", 1], ["B", 2], ["C", 3], ["D", 4], ["E", 5], ["F", 6], ["G", 6]]
ary.assoc('A') => ["A", 1]
ary.rassoc('3') => ["C", 3]
Note: these methods return the first matching array, not all of them.
See more at http://www.ruby-doc.org/core-2.1.2/Array.html
I see no point in creating a hash to locate a single value. Why not the simple, direct approach?
values = [["a", 1], ["b", 3], ["c", 7]]
values.find { |l,n| l=='b' }.last #=> 3
values.find { |l,n| n==3 }.first #=> "b"
Of course, neither of these deal with multiple values.
