Conditional key/value in a ruby hash

Question

Is there a nice (one line) way of writing a hash in ruby with some entry only there if a condition is fulfilled? I thought of

{:a => \'a\', :b => (\'b\         


        

Answer 1

My one-liner solution:

{:a => 'a'}.tap { |h| h.merge!(:b => 'b') if condition }

Answer 2

If you have multiple conditions and logic that others will need to understand later then I suggest this is not a good candidate for a 1 liner. It would make more sense to properly create your hash based on the required logic.

Answer 3

In Ruby 2.0 there is a double-splat operator (**) for hashes (and keyword parameters) by analogy to the old splat operator (*) for arrays (and positional parameters). So you could say:

{a: 'b', **(condition ? {b: 'b'} : {})}

Answer 4

>= Ruby 2.4:

{a: 'asd', b: nil}.compact
=> {:a=>"asd"}

Answer 5

You could first create the hash with key => nil for when the condition is not met, and then delete those pairs where the value is nil. For example:

{ :a => 'a', :b => ('b' if cond) }.delete_if{ |k,v| v.nil? }

yields, for cond == true:

{:b=>"b", :a=>"a"}

and for cond == false

{:a=>"a"} 

UPDATE

This is equivalent - a bit more concise and in ruby 1.9.3 notation:

{ a: 'a', b: ('b' if cond) }.reject{ |k,v| v.nil? }

UPDATE Ruby 2.4+

Since ruby 2.4.0, you can use the compact method:

{ a: 'a', b: ('b' if cond) }.compact

Answer 6

hash, hash_new = {:a => ['a', true], :b => ['b', false]}, {}
hash.each_pair{|k,v| hash_new[k] = v[1] ? v : nil }
puts hash_new