For an array like this:
a = [{a:'a',b:'3'},{a:'b',b:'2'},{a:'c',b:'1'}]
I would like to return an array containing values for :a
keys, so:
['a', 'b', 'c']
That can be done using:
a.map{|x|x[:a]}
I wonder if there is a native method in Rails or Ruby to do it like this?
a.something :a
You can do it yourself:
class Array
def get_values(key)
self.map{|x| x[key]}
end
end
Then you can do this:
a.get_values :a
#=> ["a", "b", "c"]
More than you need in this case, but from How to merge array of hashes to get hash of arrays of values you can get them all at once:
merged = a.inject{ |h1,h2| h1.merge(h2){ |_,v1,v2| [*v1,*v2] } }
p merged[:a] #=> ["a", "b", "c"]
p merged[:b] #=> ["3", "2", "1"]
Also, if you use something like Struct or OpenStruct for your values instead of hashes—or any object that allows you to get the "a" values as a method that does not require parameters—you can use the Symbol#to_proc
convenience for your map:
AB = Struct.new(:a,:b)
all = [ AB.new('a','3'), AB.new('b','2'), AB.new('c','1') ]
#=> [#<AB a="a", b="3">, #<AB a="b", b="2">, #<AB a="c", b="1">]
all.map(&:a) #=> ["a", "b", "c"]
all.map(&:b) #=> ["3", "2", "1"]
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