Changing the value of one attribute in a Ruby collection

Say for example I've got a collection like this开发者_开发知识库:

[{"name" => "Ganesh", "magic_number" => 7}, {"name" => "Comrade", "magic_number" => 2}...]

How can I change the value of ALL the magic_numbers in the collection to be the same value (e.g. 8)?

I'm sure it's using something like map or collect but I can't seem to do it at the moment and return me the whole collection with the changes, just one or the other...

Just use .each:

a = [{"name" => "Ganesh", "magic_number" => 7}, {"name" => "Comrade", "magic_number" => 2} ]
a.each { |x| x['magic_number'] = 8 }
# a is now [{"magic_number"=>8, "name"=>"Ganesh"}, {"magic_number"=>8, "name"=>"Comrade"}]

The argument to the block is a reference to the original elements so you can change them as desired. Note that this changes a in-place which I think is what you're after.

This works:

x = [{"name" => "Ganesh", "magic_number" => 7}, {"name" => "Comrade", "magic_number" => 2}]
x.map{|i| i["magic_number"] = 0; i }

=> [{"magic_number"=>0, "name"=>"Ganesh"}, {"magic_number"=>0, "name"=>"Comrade"}]