[ruby] Best way to pretty print a hash

I have a large hash with nested arrays and hashes. I would like to simply print it out so it 'readable' to the user.

I would like it to be sort of like to_yaml - that's pretty readable - but still too tech looking.

Ultimately its going to be end users who need to read these data chunks so they need to be formatted cleanly.

Any suggestions?

For large nested hashes this script could be helpful for you. It prints a nested hash in a nice python/like syntax with only indents to make it easy to copy.

module PrettyHash
  # Usage: PrettyHash.call(nested_hash)
  # Prints the nested hash in the easy to look on format
  # Returns the amount of all values in the nested hash

  def self.call(hash, level: 0, indent: 2)
    unique_values_count = 0
    hash.each do |k, v|
      (level * indent).times { print ' ' }
      print "#{k}:"
      if v.is_a?(Hash)
        puts
        unique_values_count += call(v, level: level + 1, indent: indent)
      else
        puts " #{v}"
        unique_values_count += 1
      end
    end
    unique_values_count
  end
end

Example usage:

  h = {a: { b: { c: :d }, e: :f }, g: :i }
  PrettyHash.call(h)

a:
  b:
    c: d
  e: f
g: i
=> 3

The returned value is the count (3) of all the end-level values of the nested hash.

Easy to do with json if you trust your keys to be sane:

JSON.pretty_generate(a: 1, 2 => 3, 3 => nil).
  gsub(": null", ": nil").
  gsub(/(^\s*)"([a-zA-Z][a-zA-Z\d_]*)":/, "\\1\\2:"). # "foo": 1 -> foo: 1
  gsub(/(^\s*)(".*?"):/, "\\1\\2 =>") # "123": 1 -> "123" => 1

{
  a: 1,
  "2" => 3,
  "3" => nil
}

Under Rails, arrays and hashes in Ruby have built-in to_json functions. I would use JSON just because it is very readable within a web browser, e.g. Google Chrome.

That being said if you are concerned about it looking too "tech looking" you should probably write your own function that replaces the curly braces and square braces in your hashes and arrays with white-space and other characters.

Look up the gsub function for a very good way to do it. Keep playing around with different characters and different amounts of whitespace until you find something that looks appealing. http://ruby-doc.org/core-1.9.3/String.html#method-i-gsub

Use the answers above if you're printing to users.

If you only want to print it for yourself in console, I suggest using the pry gem instead of irb. Besides pretty printing, pry has a lot of other features as well (check railscast below)

gem install pry

And check this railscast:

http://railscasts.com/episodes/280-pry-with-rails

I came here through a search engine looking for a way to print hashes to end users in a human-readable format—particularly hashes with underscores in their keys.

Here's what I ended up doing using Rails 6.0.3.4:

hash.map do |key, val|
  key.to_s.humanize + ': ' + val.to_s
end.join('; ')

# Turns {:foo_bar => 'baz', :fee_ber => :bez} into 'Foo bar: Baz; Fee ber: Bez'.

If you don't have any fancy gem action, but do have JSON, this CLI line will work on a hash:

puts JSON.pretty_generate(my_hash).gsub(":", " =>")

#=>
{
  :key1 => "value1",

  :key2 => "value2",

  :key3 => "value3"
}

In Rails

If you need

• a "pretty printed" Hash
• in e.g. the Rails.logger
• that, specifically, runs inspect on the objects in the Hash
  • which is useful if you override/define the inspect method in your objects like you're supposed to

... then this works great! (And gets better, the bigger and more nested your Hash object is.)

logger.error my_hash.pretty_inspect

For example:

class MyObject1
  def inspect
    "<#{'*' * 10} My Object 1 #{'*' * 10}>"
  end
end

class MyObject2
  def inspect
    "<#{'*' * 10} My Object 2 #{'*' * 10}>"
  end
end

my_hash = { a: 1, b: MyObject1.new, MyObject2.new => 3 }

Rails.logger.error my_hash
# {:a=>1, :b=><********** My Object 1 **********>, <********** My Object 2 **********>=>3}

# EW! ^

Rails.logger.error my_hash.pretty_inspect
# {:a=>1,
#  :b=><********** My Object 1 **********>,
#  <********** My Object 2 **********>=>3}

pretty_inspect comes from PrettyPrint, which rails includes by default. So, no gems needed and no conversion to JSON needed.

Not In Rails

If you're not in Rails or if the above fails for some reason, try using require "pp" first. For example:

require "pp"  # <-----------

class MyObject1
  def inspect
    "<#{'*' * 10} My Object 1 #{'*' * 10}>"
  end
end

class MyObject2
  def inspect
    "<#{'*' * 10} My Object 2 #{'*' * 10}>"
  end
end

my_hash = { a: 1, b: MyObject1.new, MyObject2.new => 3 }

puts my_hash
# {:a=>1, :b=><********** My Object 1 **********>, <********** My Object 2 **********>=>3}

# EW! ^

puts my_hash.pretty_inspect
# {:a=>1,
#  :b=><********** My Object 1 **********>,
#  <********** My Object 2 **********>=>3}

A Full Example

Big ol' pretty_inspected Hash example from my project with project-specific text from my inspected objects redacted:

{<***::******************[**:****, ************************:****]********* * ****** ******************** **** :: *********** - *** ******* *********>=>
  {:errors=>
    ["************ ************ ********** ***** ****** ******** ***** ****** ******** **** ********** **** ***** ***** ******* ******",
     "************ ************ ********** ***** ****** ******** ***** ****** ******** **** ********** is invalid",
     "************ ************ ********** ***** ****** ******** is invalid",
     "************ ************ ********** is invalid",
     "************ ************ is invalid",
     "************ is invalid"],
   :************=>
    [{<***::**********[**:****, *************:**, ******************:*, ***********************:****] :: **** **** ****>=>
       {:************=>
         [{<***::***********[**:*****, *************:****, *******************:**]******* :: *** - ******* ***** - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: *** - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ********* - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ********** - ********** *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ******** - *>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: **** - *******>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: *** - ********** ***** - *>=>
            {}}]}},
     {<***::**********[**:****, *************:**, ******************:*, ***********************:****] ******************** :: *** - *****>=>
       {:errors=>
         ["************ ********** ***** ****** ******** ***** ****** ******** **** ********** **** ***** ***** ******* ******",
          "************ ********** ***** ****** ******** ***** ****** ******** **** ********** is invalid",
          "************ ********** ***** ****** ******** is invalid",
          "************ ********** is invalid",
          "************ is invalid"],
        :************=>
         [{<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - ********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - ********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *******>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]*********** :: ****>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *******>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *******>=>
            {:errors=>
              ["********** ***** ****** ******** ***** ****** ******** **** ********** **** ***** ***** ******* ******",
               "********** ***** ****** ******** ***** ****** ******** **** ********** is invalid",
               "********** ***** ****** ******** is invalid",
               "********** is invalid"],
             :**********************=>
              [{<***::*******************[**:******, ************************:***]****-************ ******************** ***: * :: *** - ***** * ****** ** - ******* * **: *******>=>
                 {:errors=>
                   ["***** ****** ******** **** ********** **** ***** ***** ******* ******",
                    "***** ****** ******** **** ********** is invalid"],
                  :***************=>
                   [{<***::********************************[**:******, *************:******, ***********:******, ***********:"************ ************"]** * *** * ****-******* * ******** * ********* ******************** *********************: ***** :: "**** *" -> "">=>
                      {:errors=>["**** ***** ***** ******* ******"],
                       :**********=>
                        {<***::*****************[**:******, ****************:["****** ***", "****** ***", "****** ****", "******* ***", "******* ****", "******* ***", "****"], **:""] :: "**** *" -> "">=>
                          {:errors=>
                            ["***** ******* ******",
                             "***** ******* ******"]}}}}]}}]}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:**]******* :: ****** - ** - *********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - ********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - **********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - **********>=>
            {}},
          {<***::***********[**:*****, *************:****, *******************:***]******* :: ****** - ** - **********>=>
            {}}]}}]}}

Another solution which works better for me than pp or awesome_print:

require 'pry' # must install the gem... but you ALWAYS want pry installed anyways
Pry::ColorPrinter.pp(obj)

Using Pry you just need to add the following code to your ~/.pryrc:

require "awesome_print"
AwesomePrint.pry!

If you have JSON, I recommend JSON.pretty_generate(hash) because it is simpler than awesome_print, looks great in a pre tag, and allows for easy copying from a web page. (See also: How can I "pretty" format my JSON output in Ruby on Rails?)

Here's another approach using json and rouge:

require 'json'
require 'rouge'

formatter = Rouge::Formatters::Terminal256.new
json_lexer = Rouge::Lexers::JSON.new

puts formatter.format(json_lexer.lex(JSON.pretty_generate(JSON.parse(response))))

(parses response from e.g. RestClient)

Of all the gems I tried, show_data gem worked the best for me, I now use it extensively to log params hash in Rails pretty much all the time