Most efficient way to extract an item from a Ruby array of hashes - ruby

Question

I have some large Ruby structures that I need to quickly extract data from. I have no control over the format of the data, although I'm open to transforming it under certain circumstances. What is the most efficient way to extract a single item from the following hash, when using the displayName as the 'key'.
[
{'displayName'=>'Some Key 1', 'values'=>[1,2,3]},
{'displayName'=>'Some Key 2', 'values'=>["Some text"]},
{'displayName'=>'Some Key 3', 'values'=>["Different text","More text"]},
{'displayName'=>'Some Key 4', 'values'=>[2012-12-12]}
]
Each hash has other keys in it that I've removed to assist understanding.
The challenge is that in certain circumstances, the displayName field will need to be matched on a prefix sub-string. Does anybody have any practical experience knowing when to use .each and match manually, or .select to get the common case exact matches and fallback for the prefixes afterwards. Or is there some common trick I'm missing.

Answer 1

If you're doing this once, you'll probably just have to iterate over the set and find what you need:
row = data.find do |row|
row['displayName'] == name
end
row && row['values']
If you're doing it more than once, you should probably make an indexed structure out of it with a simple transform to create a temporary derivative structure:
hashed = Hash[
data.collect do |row|
[ row['displayName'], row['values'] ]
end
]
hashed[name]

Answer 2

You can use simple select thought it may no be as fast as it could with large sized arrays:
data = [
{'displayName'=>'Some Key 1', 'values'=>[1,2,3]},
{'displayName'=>'Some Key 2', 'values'=>["Some text"]},
{'displayName'=>'Some Key 3', 'values'=>["Different text","More text"]},
{'displayName'=>'Some Key 4', 'values'=>[2012-12-12]}
]
data.select { |e| e['displayName'] == 'Some Key 2' }.first
You can group_by the desired key instead, wich will make access faster
hashed_data = data.group_by { |e| e['displayName'] }
hashed_data['Some Key 4']
=> [{"displayName"=>"Some Key 4", "values"=>[1988]}]