Filter an array in Ruby

Question

In Ruby, I have a hash like below. How can I get the "name" of the "tag" where the tag_type is "LocationTag"? In this case, the returned value would be 'singapore'.

Is the best method just to do:

location = nil
tags.each do |t|
  if t["tag_type"] == "LocationTag" 
    location = t.name
  end
end

or does ruby have a better method for filtering hashes?

   {
      tags: [
        {
          "id": 81410,
          "tag_type": "SkillTag",
          "name": "angular.js",
          "display_name": "Angular.JS",
          "angellist_url": "https:\/\/angel.co\/angular-js"
        },
        {
          "id": 84038,
          "tag_type": "SkillTag",
          "name": "bootstrap",
          "display_name": "Bootstrap",
          "angellist_url": "https:\/\/angel.co\/bootstrap"
        },
        {
          "id": 1682,
          "tag_type": "LocationTag",
          "name": "singapore",
          "display_name": "Singapore",
          "angellist_url": "https:\/\/angel.co\/singapore"
        },
        {
          "id": 14726,
          "tag_type": "RoleTag",
          "name": "developer",
          "display_name": "Developer",
          "angellist_url": "https:\/\/angel.co\/developer"
        }
    ]
 }

mr rogers · Accepted Answer · 2014-12-26 21:01:02Z

3

This will get you the first hit:

tags.detect{|tag| tag['tag_type'] == 'LocationTag'}['name']

This will give you all hits as an array

tags.select{|tag| tag['tag_type'] == 'LocationTag'}.map{|t| t['name']}

Check out the docs for Ruby#Enumerable for more details.

Ruby#Enumerable:detect

Ruby#Enumerable:select

(Thanks @PaulRichter for the comment... it's a nice clarifying addition to the post)

answered Dec 26, 2014 at 21:01

mr rogers

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5 Comments

Paul Richter Over a year ago

Direct link to detect method

Denis de Bernardy Over a year ago

@PaulRichter: find is another alias.

mr rogers Over a year ago

I try to avoid find only because in Rails, on AR objects, find is really different than detect. So to keep things clear (for me), I try to use find when it's an AR#find and detect when it's an Enumerable. Just a matter of preference.

Paul Richter Over a year ago

It does appear that detect and find are the same thing. Anyone know the reason for the different names (assuming there is no practical difference, other than the preferential reason mr rogers mentioned)?

Denis de Bernardy Over a year ago

@PaulRichter: Best I'm aware the aliases are nothing more than a reflection of Matz's views on what is natural: en.wikipedia.org/wiki/Ruby_(programming_language)#Philosophy

Denis de Bernardy · Accepted Answer · 2014-12-26 21:17:35Z

2

You can use find to stop the iteration once you've found a result:

location = tags.find { |t| t["name"] if t["tag_type"] == "LocationTag" }

Mind the errors that got fixed in the above: t.name and = "LocationTag".

edited Dec 26, 2014 at 21:17

answered Dec 26, 2014 at 21:00

Denis de Bernardy

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