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

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