Ruby hash keys to array conditional on hash value

Question

I would like to extract hash key values to an array when a condition is met. For example, with hash h I want to extract the keys where the values are "true":

h = { :a => true, :b => false, :c =>true }

I've come up with this:

h.map {|k,v| k if v==true} - [nil]

Any alternatives?

map and select methods are aliases, so you can use one of them. — sbagdat
– sbagdat, Commented Feb 7, 2013 at 8:43
@sbagdat, to be precise, map and collect are aliases, not select. select does different job and in case of Hash returns different type: it returns Hash, while map/collect return Array. — NIA
– NIA, Commented Feb 7, 2013 at 9:01

Hauleth · Accepted Answer · 2013-02-07 08:24:11Z

15

h.select { |_, v| v }.keys

Will do the same, but in more readable way.

answered Feb 7, 2013 at 8:24

Hauleth

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4 Comments

DavB Over a year ago

That's nice, thanks. However, to return an array you need to use to_a.

Jörg W Mittag Over a year ago

keys returns an Array. What else would it return?

Drazen Over a year ago

It's a clever way but i am not sure it is a "more readable way".

Hauleth Over a year ago

Why not? Also this is more general case, as it will allow all "true" values, not only true (in Ruby, like in Scheme, anything except nil and false is true in condition, but 1 != true).

Kumar Akarsh · Accepted Answer · 2013-02-07 10:11:38Z

0

You can also do

s = {}
h.each do |k,v|
   s[k] = v if v==true
end

answered Feb 7, 2013 at 10:11

Kumar Akarsh

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