compare values in a hash and return the matching key

Question

I'm trying to look through a hash and compare it's values to an existing string and then when the match is found I want to output its key. I trying to write this in a code block and output the result to the console.

officer.name = "Dave"

@hash = { "Tom" => "97", "Dave" => "98", "John" => "99" }

@hash.each { |key, value| do
    if #{key} == officer.name
        puts "id: #{value}"
    else
        puts "no match"
    end
}

Right now my console outputs:

 id: 97
 no match
 id: 98
 no match
 id: 99
 no match

I'm trying to get it to output just the value of #{value} based on it's matching #{key}, which in this case would be Dave. So for the above example I want my console to spit just the number 98 or "no match".

Why wouldn't you just access the value using the key? Why iterate? Also, your title is the reverse of your code and text. — Dave Newton, Oct 03 '12 at 14:20
`if #{key} == officer.name` : everything after the `#` is a comment. — steenslag, Oct 03 '12 at 14:54

score 6 · Accepted Answer · answered Oct 03 '12 at 14:19

6

This is a hash! You can do what you attempt way more efficiently:

officer.name = "Dave"

@hash = { "Tom" => "97", "Dave" => "98", "John" => "99" }

unless @hash.key?(officer.name) 
  puts "no match"
else 
  puts "id: #{@hash[officer.name]}"
end

answered Oct 03 '12 at 14:19

Ivaylo Strandjev

69,226
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Why putting an `unless else end` statement... ? – oldergod Oct 04 '12 at 00:13

score 3 · Answer 2 · answered Oct 03 '12 at 14:17

3

Is it because you forgot the " ?

if "#{key}" == officer.name

but you could just do

if key == officer.name

answered Oct 03 '12 at 14:17

oldergod

15,033
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Or you don't need to interpolate at all? – Dave Newton Oct 03 '12 at 14:20

score 2 · Answer 3 · answered Oct 03 '12 at 14:18

2

officer.name = "Dave"

@hash = { "Tom" => "97", "Dave" => "98", "John" => "99" }

@hash.each do |key, value|
  if key == officer.name
    puts key
  else
    puts "no match"
  end
end

This should work

answered Oct 03 '12 at 14:18

Anthony Alberto

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score 2 · Answer 4 · answered Oct 03 '12 at 14:44

2

@hash.has_key?(officer.name) ? @hash[officer.name] : "no match"

answered Oct 03 '12 at 14:44

saihgala

5,724
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score 1 · Answer 5 · answered Oct 03 '12 at 14:52

When doing hash lookups by key, avoid #[]. Favor #fetch instead:

officer.name = "Dave"
@hash = { "Tom" => "97", "Dave" => "98", "John" => "99" }
puts @hash.fetch(officer.name, 'no match')

#fetch allows you to specify a default value other than nil, which will prevent unexpected nils from hash lookups from throwing the all-too-common NoMethodError.

score 1 · Answer 6 · answered Jan 23 '13 at 23:07

this works too. slight edit from original post. it prints out answer for each pair though and doesn't identify which pair the answer refers to.

officer = "Dave"

@hash = { "Tom" => "97", "Dave" => "98", "John" => "99" }

@hash.each do |key, value|
    if key == officer
    puts key
  else
    puts "no match"
  end
end

compare values in a hash and return the matching key

6 Answers6