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I have a nested hash inside a set, in my rails app, and I'm trying to access all the values of one key in an enumerable way.

So I have a set which looks like this (not the actual names of my keys and values)

my_set=[{:foo=>"lion", :boolean1=>true, :boolean2=>false, :boolean3=>true},
         {:foo=>"monkey", :boolean1=>false, :boolean2=>true, :boolean3=>true},
         {:foo=>"elephant", :boolean1=>false, :boolean2=>true, :boolean3=>true}
         ]

I want to be able to iterate over all the values of foo. Is there a better way to do it than as follows?

foo_array=[]
my_set.each do |hash|
  foo_array<<hash[:foo]
end

I haven't been able to find anything on accessing all the values of :foo in my set, only on accessing individual elements in the nested enumerables, which I know how to do. Thank you.

ctaymor
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2 Answers2

2

I think the simplest way would be this:

foo_array = my_set.map { |hash| hash[:foo] }
lurker
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1

First, your definition for my_set isn't valid.

Fixing that, I'd use:

my_set=[
  {:foo=>"lion", :boolean1=>true, :boolean2=>false, :boolean3=>true},
  {:foo=>"monkey", :boolean1=>false, :boolean2=>true, :boolean3=>true},
  {:foo=>"elephant", :boolean1=>false, :boolean2=>true, :boolean3=>true}
]

foo_array = my_set.map{ |h| h[:foo] } # => ["lion", "monkey", "elephant"]

Your code works fine too though:

foo_array=[]
my_set.each do |hash|
  foo_array<<hash[:foo]
end
foo_array # => ["lion", "monkey", "elephant"]

It's just a different way of doing it.

the Tin Man
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  • Thanks. It's not actually how I'm declaring the set, the set is declared with Set.new and then the hashes are merged into it iterating over a different array. I was trying to represent how the set ends up being when I need to get foo out of it. I think the mapping version is better because it's less code for the same thing, though. – ctaymor Jul 23 '13 at 16:28
  • It's really important that you show exactly how you define your data. Using a Set has side-effects and implications that aren't there for Arrays. I'm not sure why you'd use Set though, as it's not going to buy you anything. – the Tin Man Jul 23 '13 at 17:59
  • okay, thank you. I've edited the question to make that clearer, and will try to keep that in mind in the future. I'm pretty new to this. I'm using Set instead of Array because I want its side effect of not allowing duplicates. I don't want any duplicates of my hash. The Set is populated when iterating over an array in which multiple items could potentially push the same thing into the Set if it were an array. With a Set, I only get one occurrence of each hash in the set. – ctaymor Jul 23 '13 at 21:15