从哈希中删除 nil 值

Question

I am looking to remove keys from hash that have nil value. article is a class storing each article, and attributes method stores the article as hash.

Expected Result:

{"articles":[{"results":[{"author":null,"title":"Former bar manager jailed for preying on homeless 14-year-old girl","summary":"<p><img src=\"http://images.theage.com.au/2015/08/24/6790912/Thumbnail999662740gisd08image.related.thumbnail.320x214.gj68pg.png1440386418031.jpg-90x60.jpg\" width=\"90\" height=\"60\" style=\"float:left;margin:4px;border:0px\"/></p>A man who preyed on a 14-year-old girl he came across living on the streets of&#160;Wodonga has been jailed for nine months.","images":null,"source":null,"date":"Mon, 24 Aug 2015 03:20:21 +0000","guid":"<guid isPermaLink=\"false\">gj68pg</guid>","link":"http://www.theage.com.au/victoria/former-bar-manager-jailed-for-preying-on-homeless-14yearold-girl-20150824-gj68pg.html","section":null,"item_type":null,"updated_date":null,"created_date":null,"material_type_facet":null,"abstract":null,"byline":null,"kicker":null}]}]}

Looking to remove null values from the above output.

def attributes
  hash = {
    "author" => @author,
    "title" => @title,
    "summary" => @summary,
    "images" => @images,
    "source" => @source,
    "date" => @date
  }
  hash = {}
  count = 0
  article.attributes.each do |key,value|
    if value == nil
      hash[count] = article.attributes.delete(key)
      count += 1
    end
  end
  hash.to_json

The result is as below:

{"0":null,"1":null,"2":null,"3":null,"4":null,"5":null,"6":null,"7":null,"8":null,"9":null,"10":null}

Answer 1

How about trying:

hash = article.attributes.select {|k, v| v }

If the value is false or nil , the attribute will be ignored.

If you want to keep the false value and only eliminate nil , you could run:

hash = article.attributes.select {|k, v| !v.nil? }

Answer 2

If you're on Ruby >= 2.4.6, you can use compact .

https://apidock.com/ruby/v2_4_6/Hash/compact

Example:

hash = {:foo => nil, :bar => "bar"}
=> {:foo=>nil, :bar=>"bar"}
hash.compact
=> {:bar=>"bar"}
hash
=> {:foo=>nil, :bar=>"bar"}

There's also compact! which removes nil values, or nil if no values in the hash were nil (from version >= 2.5.5).

https://apidock.com/ruby/v2_4_6/Hash/compact%21

Example:

hash
=> {:foo=>nil, :bar=>"bar"}
hash.compact!
=> {:bar=>"bar"}
hash
=> {:bar=>"bar"}
hash.compact!
=> nil

Answer 3

You can remove all the nil values from a hash namely "h":

h.delete_if { |k, v| v.nil? }

and you can use this one to remove empty values, too:

h.delete_if { |k, v| v.nil? || v.empty? }

Answer 4

In my case I use refinements to Hash class

module HashUtil
    refine Hash do
        # simple but can not adapt to nested hash
        def squeeze
            select{|_, v| !v.nil? }
        end
        # complex but can adapt to nested hash
        def squeeze_deep
            each_with_object({}) do |(k, v), squeezed_hash|
                if v.is_a?(Hash)
                    squeezed_hash[k] = v.squeeze
                else
                    squeezed_hash[k] = v unless v.nil?
                end
            end
        end
    end
end

class Article
    using HashUtil
    def attributes
        hash = {
            "author" => @author,
            "title" => @title,
            "summary" => @summary,
            "images" => @images,
            "source" => @source,
            "date" => @date
        }
        hash.squeeze
    end
end

Answer 5

The given input is valid JSON, and the question has the JSON tag, so I'd like to offer a generic solution to the problem of recursively eliminating keys in JSON objects, wherever they occur, and no matter what the input JSON may be.

The solution is written in a new JSON-oriented programming language, jq, but even if you cannot use jq, the solution is so brief and elegant that it may suggest an implementation to the general problem in your language of choice.

Here it is - a one-liner:

walk( if type == "object" then with_entries( select(.value != null) ) else . end)

This presupposes jq version 1.5 (see https://stedolan.github.io/jq/ ).

If you have an older version of jq, the definition of walk/1 can easily be added. (See eg Transforming the name of key deeper in the JSON structure with jq )