How can I assign multiple values to a hash key?

问题:

For the sake of convenience I am trying to assign multiple values to a hash key in Ruby. Here's the code so far

myhash = { :name => ["Tom" , "Dick" , "Harry"] }

Looping through the hash gives a concatenated string of the 3 values

Output:

name : TomDickHarry

Required Output:

:name => "Tom" , :name => "Dick" , :name => "Harry"

What code must I write to get the required output?

回答1:

You've created a hash with the symbol name as the key and an array with three elements as the value, so you'll need to iterate through myhash[:name] to get the individual array elements.

回答2:

myhash.each_pair {|k,v| v.each {|n| puts "#{k} => #{n}"}}
#name => Tom
#name => Dick
#name => Harry

The output format is not exactly what you need, but I think you get the idea.

回答3:

The answers from Rohith and pierr are fine in this case. However, if this is something you're going to make extensive use of it's worth knowing that the data structure which behaves like a Hash but allows multiple values for a key is usually referred to as a multimap. There are a couple of implementations of this for Ruby including this one.

回答4:

re: the issue of iterating over selective keys. Try using reject with the condition inverted instead of using select.

e.g. given:

{:name=>["Tom", "Dick", "Harry"], :keep=>[4, 5, 6], :discard=>[1, 2, 3]}

where we want :name and :keep but not :discard

with select:

myhash.select { |k, v| [:name, :keep].include?(k) }
=> [[:name, ["Tom", "Dick", "Harry"]], [:keep, [4, 5, 6]]]

The result is a list of pairs.

but with reject:

myhash.reject { |k, v| ![:name, :keep].include?(k) }
=> {:name=>["Tom", "Dick", "Harry"], :keep=>[4, 5, 6]}

The result is a Hash with only the entries you want.

This can then be combined with pierr's answer:

hash_to_use = myhash.reject { |k, v| ![:name, :keep].include?(k) }
hash_to_use.each_pair {|k,v| v.each {|n| puts "#{k} => #{n}"}}