Ruby Quicktips

Got a hash of values you want to convert into a url query string? Use [the to_query method](http://api.rubyonrails.org/classes/Object.html#method-i-to_query "Object"):

"http://www.example.com?" + { language: "ruby", status: "awesome" }.to_query # => "http://www.example.com?language=ruby&status=awesome"

Want to do it in reverse? Use [CGI.parse](http://www.ruby-doc.org/stdlib-1.9.3/libdoc/cgi/rdoc/CGI.html#method-c-parse "Class: CGI (Ruby 1.9.3)"):

require 'cgi' # Only needed for IRB, Rails already has this loaded CGI::parse "language=ruby&status=awesome" # => {"language"=>["ruby"], "status"=>["awesome"]}

Let's say you have a form like this for uploading a CSV file:

<%= form_tag csv_import_path, :multipart => true do %> <%= file_field_tag :file, :accept => "text/csv" %> <%= submit_tag "Upload" %> <% end %>

And your controller action looks like this:

require 'csv' def csv_import file_data = params[:file].read csv_rows = CSV.parse(file_data) csv_rows.each do |row| # do something with each row end respond_to do |format| format.html { redirect_to your_path, :notice => "Successfully imported the CSV file." } end end

How would you test this functionality?

You can't use fixture_file_upload and stick a sample file in test/fixtures/files/ (as often suggested - e.g. here on SO). That's because CSV and YAML files will be imported as fixtures into the test database as soon as you run tests. E.g., this would not work:

def test_file_upload post :csv_import, :file => fixture_file_upload('files/new_users.csv','text/csv') end

But what you can do is to use the Tempfile and Rack::Test::UploadFile classes and manually create a CSV file and supply this to the post (or put) method:

Ever wanted to try out any of Rails' view helper methods in the console? Just include `ActionView::Helpers` after starting the Rails console:

Creating a [regular expression](http://www.ruby-doc.org/core-1.9.3/Regexp.html "Class: Regexp (Ruby 1.9.3)") using the `r{}` literals can for example be helpful when matching URLs, because you don't have to escape slashes:

The [Hash::[] class method](http://www.ruby-doc.org/core-1.9.3/Hash.html#method-c-5B-5D "Class: Hash (Ruby 1.9.3)") can be used in addition to the [splat operator](http://pivotallabs.com/users/nick/blog/articles/438-ruby-pearls-vol-1-the-splat "nick - Ruby Pearls vol. 1 - The Splat") to create a hash from an array.

As Aditya Sanghi notes in ["Quickly convert an Array to a Hash"](http://rubyquicktips.com/post/17306181714/quickly-convert-an-array-to-a-hash "Ruby Quicktips - Quickly convert an Array to a Hash"), a very quick way to convert an Array to a Hash, is to use Rails' [Enumerable#index_by](http://api.rubyonrails.org/classes/Enumerable.html#method-i-index_by "Enumerable"):

As Brich Thompson notes in the comments on ["Convert between number bases easily"](http://rubyquicktips.com/post/18935873770/convert-between-number-bases-easily "Ruby Quicktips - Convert between number bases easily"), you can also convert a number string in any base to a decimal number with the [String#to_i](http://www.ruby-doc.org/core-1.9.3/String.html#method-i-to_i "Class: String (Ruby 1.9.3)") method:

[1,2,3].each_with_object(1).map(&:+) # => [2, 3, 4] # Same outcome, even shorter [1, 2, 3].map(&1.method(:+)) # => [2, 3, 4]

Enumerable#each_with_object is quite similar to Enumerable#inject, yet slightly different. From the Ruby 1.9 and Rails 3 API docs:

Iterates the given block for each element with an arbitrary object given, and returns the initially given object.

Iterates over a collection, passing the current element and the memo to the block. Handy for building up hashes or reducing collections down to one object.

evens = (1..10).each_with_object([]) {|i, a| a << i*2 } #=> [2, 4, 6, 8, 10, 12, 14, 16, 18, 20] %w(foo bar).each_with_object({}) { |str, hsh| hsh[str] = str.upcase } # => {'foo' => 'FOO', 'bar' => 'BAR'}

As BiHi noted on this tip on Enumerable#inject, its example can be slightly simplified using each_with_object instead of inject:

To mark deprecated code in Ruby simply add a comment to the rdoc and call the Kernel#warn method. For example:

class Foo # DEPRECATED: Please use useful instead. def useless warn "[DEPRECATION] `useless` is deprecated. Please use `useful` instead." useful end def useful # ... end end

If you're using Yard instead of rdoc, your doc comment should look like this:

# @deprecated Please use {#useful} instead

Also, don't forget to remove the deprecated method in some future release.

We can define a new Hash in a smart way by using [Hash#new](http://ruby-doc.org/core-1.9.3/Hash.html#method-c-new "Class: Hash (Ruby 1.9.3)") and passing it a block:

h = Hash.new {|hash,key| hash[key] = hash[key-1] + hash[key-2]} h[1] = 0 h[2] = 1 puts h[3] #=> 1 puts h[100] #=> 218922995834555169026

Here an example of famous [Collatz Conjecture](http://en.wikipedia.org/wiki/Collatz_conjecture "Collatz conjecture - Wikipedia, the free encyclopedia"):

h = Hash.new {|hash,n| hash[n] = 1 + (n.odd? ? hash[3*n+1] : hash[n/2])} h[1] = 1 puts h[100] #=> 26 puts h[1000] #=> 112

Wrap a block of code within `=begin` and `=end` to comment it out.

# the comment format you're used to puts "I am evaluated" =begin puts "I" puts "am" puts "commented" puts "out" =end

**Aim:** perform a method chaining based on hash **Required operation:**

ErrorLog.event_eq([3, 7]).subdomain_like("default").user_id_eq(100)

**Given:**

search_opts = { :event_eq => [3, 7], :subdomain_like => "default", :user_id_eq => 100 }

**Solution:**

search_opts.inject(ErrorLog) { |memo, (k, v)| memo.send(k, v) }

If you're not sure what files a Rails Generator would create for you, just add the `-p` option (or `--pretend`) for a dry run:

It's often a requirement in various projects to convert numbers from decimal to text representations of several other bases, such as hexadecimal or binary. Did you know you can convert to any base from 2 to 36 in one line in Ruby? Using the [Fixnum#to_s](http://www.ruby-doc.org/core-1.9.3/Fixnum.html#method-i-to_s "Class: Fixnum (Ruby 1.9.3)") method, you can quickly convert any Fixnum object to the textual format of another base:

255.to_s(36) #=> "73" 255.to_s(16) #=> "ff" 255.to_s(2) #=> "11111111"

To add on corresponding elements of several arrays:

a = [1, 2, 3] b = [4, 5, 6] c = [7, 8, 9] [a, b, c].transpose.map { |x| x.reduce :+ } # => [12, 15, 18]

Given a number of arrays, each contains same number of arrays with the same length. To merge corresponding arrays:

a = [ [1, 2], [3, 4] ] b = [ [5, 6], [7, 8] ] c = [ [9, 10], [11, 12] ] (a.transpose + b.transpose + c.transpose).transpose # => [[1, 2, 5, 6, 9, 10], [3, 4, 7, 8, 11, 12]]

To do the same job, but with arrays that are not necessarily equal in length:

a = [ [1], [2, 3] ] b = [ [4, 5], [] ] c = [ [6,7,8], [9, 10, 11, 12] ] [a, b, c].transpose.map { |x| x.reduce :+ } # => [[1, 4, 5, 6, 7, 8], [2, 3, 9, 10, 11, 12]]