So I don’t know why I give updates here about one of the smallest projects – map_by_method.

Probably, its because it doesn’t deserve a Google Group or even a webpage really. It should probably be integrated into activesupport gem or something.

Except, it just never seemed to 100% work.

That is, it go more blog coverage than anything else, but wasn’t always useful. Yeah, a like Miss South Carolina.

BUT Version 0.8.2 is now out. It fixes – I believe – all known problems – I think.

gem install map_by_method

In your code (or config/environment.rb for rails):

gem 'map_by_method', '>=0.8.2'
require 'map_by_method'

I added a few more iterator methods too: sort_by, group_by, and index_by.

>> Conference.find(1).conference_sessions.group_by_from
=> returns all MyConfPlan conference sessions grouped by start time, for RailsConf2007

MyConfPlan…

Oh yes it sold. Announcement coming soon.

Plus, a link to the code – as it is being open sourced by its new owner. Sweet!

Well… sweet for you. I already had access to the code.

Next on the todo list

Add something similar to Ambition by Err “we-write-so-many-cool-projects-I-don’t-know-how-we-find-time-to-maintain-them-all” the Blog, Chris and PJ.

I’d kind link something like:

Conference.select { |c| c =~ "Rails").sort_by_name

Which would behave like:

>> Conference.select {|c| c.name =~ /Rails/}.sort_by(&:name).to_sql
=> "SELECT * FROM conferences WHERE conferences.\"name\" ~ 'Rails' ORDER BY conferences.name"

Oh well, perhaps we can talk about it during RailsConf Europe, when I get the microphone to talk about such tom-foolery and hi-jinx: Meta-Magic in Rails: Become a Master Magician

Related posts:

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2. map_by_method now works with ActiveRecord associations I was always annoyed that map_by_method was broken for ActiveRecord...
3. Welcome to the future Welcome to anyone visiting from DHH’s blog and other corners...

That’s the magic of Open Source Software. [/end sarcasm]

So now, the following example works like it should:

$ gem install map_by_method
$ console
> require 'map_by_method'  # stick this in your environment.rb for Rails
> user = User.find_by_name "Dr Nic"
> user.companies.map_by_name
=> ['Dr Nic Academy', 'Dr Nic Institute of Being Silly']
> user.companies.map_by_id_and_name
=> [[1, 'Dr Nic Academy'], [9, 'Dr Nic Institute of Being Silly']]

Recap: why use map_by_method?

Try the following example:

> user.companies.map_by_employees.flatten
=> list of all employees of user

Versus:

> user.companies.map { |company| company.employees}.flatten
or
> user.companies.map(&:employees).flatten

Or compare:

> user.companies.map_by_id_and_name
=> [[1, 'Dr Nic Academy'], [9, 'Dr Nic Institute of Being Silly']]

Versus:

> user.companies.map { |company| [company.id, company.name]}

That is, it looks and feels just like ActiveRecord’s #find method, with its find_by_first_name_and_last_name magic.

Summary

No {, }, |, &, or : required. Just clean method names.

Bonus other gem

In the spirit of ActiveRecord hacks, there is to_activerecord:

$ gem install to_activerecord
$ console
> require 'to_activerecord'  # stick this in your environment.rb for Rails
> [1,2,3].to_user
=> [list of User with id's 1,2,3]

To me, this suffix operator reads cleaner than the traditional:

> User.find([1,2,3])

For example, if you want to perform an operation on the list of Users:

> ids = [1,2,3]
> ids.to_user.map_by_name
=> ['Dr Nic', 'Banjo', 'Nancy']

Versus:

> User.find(ids).map_by_name

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>> p.account.transfers.map_amount # amount method mapped to all Transfers
=> [1878.35, 433.0, 433.0, 433.46, 433.46, 433.46, 433.46, 433.46, 300.0, 300.0]
>> p.account.transfers.map_date.map_to_s # date method mapped to all Transfers, and the Dates mapped into strings
=> ["2003-05-27", "2003-06-23", "2003-06-27", "2003-07-04", "2003-07-11", "2003-07-18", "2003-07-25", "2003-08-08", "2003-09-25", "2003-10-03"]

But if you want the amount and date methods mapped at the same you’ve been plain out of luck, and forced to use the uglier block syntax:

>> p.account.transfers.map {|t| [t.amount, t.date]}

Due to demand-by-inspiration (that is, I just thought of it), you can now use _and_ to join method names together, thusly:

>> p.account.transfers.map_date_and_amount
[[#<Date: 4905573/2,0,2299161>, 1878.35],
 [#<Date: 4905627/2,0,2299161>, 433.0],
 [#<Date: 4905635/2,0,2299161>, 433.0],
 [#<Date: 4905649/2,0,2299161>, 433.46],
 [#<Date: 4905663/2,0,2299161>, 433.46],
 [#<Date: 4905677/2,0,2299161>, 433.46],
 [#<Date: 4905691/2,0,2299161>, 433.46],
 [#<Date: 4905719/2,0,2299161>, 433.46],
 [#<Date: 4905815/2,0,2299161>, 300.0],
 [#<Date: 4905831/2,0,2299161>, 300.0]]
>> p.account.transfers.map_date_and_amount.map_map_to_s
[["2003-05-27", "1878.35"],
 ["2003-06-23", "433.0"],
 ["2003-06-27", "433.0"],
 ["2003-07-04", "433.46"],
 ["2003-07-11", "433.46"],
 ["2003-07-18", "433.46"],
 ["2003-07-25", "433.46"],
 ["2003-08-08", "433.46"],
 ["2003-09-25", "300.0"],
 ["2003-10-03", "300.0"]]

Note the dubious/amusing use of map_map_to_s to apply to_s to the inner arrays. That is, map_to_s is mapped to each inner array.

Want this extended map_by_method magic? Version 0.5 of map_by_method is ready via gem install map_by_method now (or direct download)

Bonus use

Make simple arrays for drop-down lists based on id and a string name field of a list of objects.

>> User.find(:all).map_id_and_firstname
=> [[1, "Glenda"], [2, "Brenda"], [3, "Yas"], [4, "Osborne"], [5, "Gary"], [6, "Anthony"], [7, "Jackie"]]

Debugging use

Some of my Transfer rows had amounts of zero. This was just stupid, but as the initial data was being migrated from a variety of sources I needed to figure out where it was coming from.

“I wonder which account owner(s) this erroneous data comes from?”

> zero_transfers = Transfer.find(:all,:conditions => ['amount < 10 and amount > -10'])
> zero_transfers.map_from_account.map_owner.map_name
["Brenda",
"Brenda",
"Brenda",
"Brenda",
"Brenda"]

And I now knew which files to start cleaning up before re-importing all the data again.

Data investigation in the console/irb becomes almost fun.

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I got tired of typing require 'pp' and the like each time I loaded up my console, that I was joyed to discover I could configure it: using the .irbrc file (win32 explanation below).

Here is mine:

require 'irb/completion'
require 'map_by_method'
require 'what_methods'
require 'pp'
IRB.conf[:AUTO_INDENT]=true

Here is what each line does:

Line 1 – Auto-completion in IRB

You can discover what methods can be called on an object. Double-TAB is your “exploration” combo.

irb(main):001:0> "hello".to_<double TAB here>
.to_a    .to_f    .to_i    .to_s    .to_str  .to_sym
irb(main):003:0> a = "hello"
=> "test"
irb(main):004:0> a.t<double TAB here>
a.taint     a.to_f      a.to_str    a.tr!       a.type
a.tainted?  a.to_i      a.to_sym    a.tr_s
a.to_a      a.to_s      a.tr        a.tr_s!

Not understanding this? Watch the video

Line 2 – Map by Method

When in the console its great to be able to explore and manipulate data as quickly as possible. The Map by Method (previously called Map by Pluralisation) is wizardly for quick-to-type array manipulations.

See the original and demo articles.

To install:

gem install map_by_method

Line 3 – MethodFinder/Object.what?

Ever asked: “if I have an object, what method can I call on it to get that result?”

See if this suits your console cravings:

> 3.45.what? 3
3.45.truncate == 3
3.45.to_i == 3
3.45.prec_i == 3
3.45.floor == 3
3.45.to_int == 3
3.45.round == 3
=> ["truncate", "to_i", "prec_i", "floor", "to_int", "round"]
> 3.45.what? 4
3.45.ceil == 4
=> ["ceil"]
> 3.55.what? 4
3.55.ceil == 4
3.55.round == 4
=> ["ceil", "round"]

Just what you need in the console.

I’ve gemified a library found on _why’s blog by Nikolas Coukouma.

To install:

gem install what_methods

Line 4 – pretty print

pp = pretty print – wondeful in the console for exploring objects that are visually large.

Thusly demonstrated:

> me = {:name => "Nic Williams", :country => "Netherlands", :city => "Amsterdam", :tags => %w(ruby rails javascript)}
=> {:country=>"Netherlands", :name=>"Nic Williams", :city=>"Amsterdam", :tags=>["ruby", "rails", "javascript"]}
irb(main):017:0> pp me
{:country=>"Netherlands",
 :name=>"Nic Williams",
 :city=>"Amsterdam",
 :tags=>["ruby", "rails", "javascript"]}
=> nil

It prints, and its pretty.

Line 5 – auto-tabbing turned on

Auto-tabbing is the console’s way of trying to help your code look pretty by indenting your blocks, etc.

It’s only primitive, but better than a kick in the teeth.

> [1,2,3].each do |a|
*     puts a
>   end
1
2
3
=> [1, 2, 3]

.irbrc for Win32

Create a file called anything you like (e.g. “_irbrc” or “irb.rc”) and place it anywhere you like (say C:\Documents and Settings\), and set that full path to the ENV variable IRBRC, e.g. C:\Documents and Settings\\_irbrc

More ideas at the bottom of this.

Epilogue

Any other useful libraries to include in irb/console?

[1] You can run irb from anywhere, but to use console for a specific rails app, you need to point to the console script for that app, e.g ruby script/console from the rails app root folder.

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I don’t like you [1]. You don’t share code. I know, I know, you’ve had good reasons – you don’t know how to create a Ruby gem, how to upload it to a gem server like RubyForge, and you’re a chicken. Today we’ll remove the first of these minor roadblocks, with a New Gem Generator!

Now you can take any library or Rails plugin or command line application, gemify it, and easily share it with the Ruby world. With gems you get in-built version support (you can specify which version of a gem you want when you use it via the require_gem method), an encapsulated, consistent folder structure for your bin/lib/test folders, and you get cross-platform support for bin apps. Too much niftiness to ignore, really.

The New Gem Generator is like the rails command for rails applications, but it creates the folders and starting files for a new gem. It’s called newgem.

Tutorial

Aim

To convert the Map by Method (previously called Map by Pluralisation) library into a gem.

See original and demo articles. Sex on a stick – soon to be gemified before your very eyes. (Download instructions for the prebuilt gem)

Installation

> gem install newgem

Download from rubyforge if you have firewall problems (as I do at work) and need to get the gem explicitly first. THEN run the above command in the folder you saved the gem.

Create new gem

> newgem map_by_method
creating: map_by_method
creating: map_by_method/CHANGELOG
creating: map_by_method/README
creating: map_by_method/lib
creating: map_by_method/lib/map_by_method
creating: map_by_method/lib/map_by_method.rb
creating: map_by_method/lib/map_by_method/version.rb
creating: map_by_method/Rakefile
creating: map_by_method/test
creating: map_by_method/test/all_tests.rb
creating: map_by_method/test/test_helper.rb
creating: map_by_method/test/map_by_method_test.rb
creating: map_by_method/examples
creating: map_by_method/bin

Copy in the library

The generated lib/map_by_method.rb file looks like:

Dir['map_by_method/**/*.rb'].sort.each { |lib| require lib }

This will automatically include (require), in alphabetical order, the files in the
lib/map_by_method folder. If you need the files required in a specific order, then do it explicitly here, for example:

require 'foo'
require 'bar'
require 'tar'

or

%w(foo bar tar).each {|lib| require lib}

For this gem there won’t be any additional library files, so we’ll just copy in the following code into the lib/map_by_method.rb file and remove the library loading code.

module MapByMethod
  def self.included(base)
    super

    base.module_eval <<-EOS
      def method_missing(method, *args, &block)
        super
      rescue NoMethodError
        error = $!
        begin
          re = /(map|collect|select|each|reject)_([\\w\\_]+\\??)/
          if (match = method.to_s.match(re))
            iterator, callmethod = match[1..2]
            return self.send(iterator) {|item| item.send callmethod}
          end
          return self.map {|item| item.send method.to_s.singularize.to_sym}
        rescue NoMethodError
          nil
        end
        raise error
      end
    EOS
  end
end

unless String.instance_methods.include? "singularize"
  class String
    def singularize
      self.gsub(/e?s\Z/,'')
    end
  end
end

Array.send :include, MapByMethod

Package your gem into a .gem file

From the root folder of your gem run rake package:

> rake package
(in C:/InstantRails/ruby_apps/map_by_method)
rm -r .config
  Successfully built RubyGem
  Name: map_by_method
  Version: 0.0.1
  File: map_by_method-0.0.1.gem
mv map_by_method-0.0.1.gem pkg/map_by_method-0.0.1.gem

Tada! You are the owner of a gem.

Install your gem onto your machine

Your Ruby (and Rails) applications can only use the gemified libraries once you have installed the packaged gem. This is the same for other people who will use your gem.

Typically you install a gem from a remote gem server such as rubyforge. Today, you will install the gem locally:

> gem install pkg/map_by_method-0.0.1.gem
Attempting local installation of 'pkg/map_by_method-0.0.1.gem'
Successfully installed map_by_method, version 0.0.1
Installing RDoc documentation for map_by_method-0.0.1...

Note that it created and installed RDoc documentation for the library too. Each user automatically has a copy of the generated documentation for your libraries (if you actually added documentation to your code).

Unit testing

Look in the test folder and see that it has created a map_by_method_test.rb unit test file to get you started. Put tests in there. Add more test files. Run rake test from the project’s root folder and watch all your tests succeed or fail. Be good.

Version numbers

Note that the generated gem is map_by_method-0.0.1.gem. The 0.0.1 is the version number of the gem, and you can easily change this as you wish as you gem takes on new features and fixes.

There are two common version number formats:

X.Y.Z – X = major release number, Y = minor release number, Z = patch/bug fix number

or

X.Y.Z.svn = svn is the subversion number at the time the gem was released.

The latter is the default implementation generated by newgem. If you want the simpler version number format (the 1st one), then remove the following line from your Rakefile (around line 13):

REV = File.read(".svn/entries")[/committed-rev="(\d+)"/, 1] rescue nil

Your gem has a prebuilt mechanism for specifying the X.Y.Z portion of the version number.

Go to lib/map_by_method/version.rb

module MapByMethod #:nodoc:
  module VERSION #:nodoc:
    MAJOR = 0
    MINOR = 0
    TINY  = 1

    STRING = [MAJOR, MINOR, TINY].join('.')
  end
end

Change MINOR and TINY to:

    MINOR = 1
    TINY  = 0

And repackage and reinstall your gem:

> rake package
(in C:/InstantRails/ruby_apps/map_by_method)
rm -r .config
  Successfully built RubyGem
  Name: map_by_method
  Version: 0.1.0
  File: map_by_method-0.1.0.gem
mv map_by_method-0.1.0.gem pkg/map_by_method-0.1.0.gem

> gem install pkg/map_by_method-0.1.0.gem
Attempting local installation of 'pkg/map_by_method-0.1.0.gem'
Successfully installed map_by_method, version 0.1.0
Installing RDoc documentation for map_by_method-0.1.0...

And you’re done. Next you would upload your gem to a gem server such as RubyForge, or one your company runs internally to share gems via the “gem install” mechanism.

map_by_method already on RubyForge

If you want the map_by_method gem, its already on RubyForge, so you can remotely install it:

gem install map_by_method

Inspiration

Jay Fields created a great “ruby application setup” script.

[1] That’s not true. I do like you.

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The other day I introduced a new syntax idea that I call “map by pluralisation”. Everyday I use it in code and in the console/irb I fall more in love with its simplicity – both to type and to read.

The following are all equivalent:

>> BankTransaction.columns.names  # map by pluralisation
=> ["id", "amount", "date", "description", "balance"]
>> BankTransaction.columns.name   # singular works too
=> ["id", "amount", "date", "description", "balance"]
>> BankTransaction.columns.map_name  # merge collector (map) + operation (name is method of BankTransaction object)
=> ["id", "amount", "date", "description", "balance"]
>> BankTransaction.columns.collect_name  # merge collector (collect) + operation
=> ["id", "amount", "date", "description", "balance"]

All of which are easier to read and quicker to type than the current equivalents:

>> BankTransaction.columns.map {|p| p.name}  # standard map
=> ["id", "amount", "date", "description", "balance"]
>> BankTransaction.columns.map &:name  # Symbol.to_proc
=> ["id", "amount", "date", "description", "balance"]

You can now type:

>> BankTransaction.columns.select_primary  # merge collector (select) and operator (primary returns true/false on a Column object)
=> [#<...MysqlColumn:0x3c8a4f0 @limit=11, @sql_type="int(11)", @primary=true, @type=:integer, @number=true, @name="id">]

Instead of:

>> BankTransaction.columns.select {|c| c.primary}
>> BankTransaction.columns.select &:primary

Use with ActiveRecords

“Map by pluralisation” is truly wonderful in the console for exploring and collecting data models.

Without knowing a thing about the data model, I bet you can understand either of the following:

@transactions = BankTransaction.find :all, :conditions => ['date = ?', Date.today], :include => [:accounts => [:owner]]
return @transactions.collect_accounts.select_overdrawn?.collect_owner.full_names

Answer: the full name of each owner of an overdrawn bank accounts for all today’s bank transactions.

It reads well as there is a minimum of {, }, |, &, : characters.

Download

Code available here

Tip for use with ActiveRecord Associations

You may need to cast associations to Arrays.

@account.transactions.to_a.map_dates

The result of the transactions assocation on the Account class is not an Array. My initial attempts to provide the “map by pluralisation” code (a method_missing) didn’t work, and casting it to an explicit Array using to_a seemed simple and harmless.

Discussion of Syntax Ideas

Ruby Forum

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Beginner’s Guide to Mapping

Need to invoke a method on each object in an array and return the result?

# call 'to_i' on each item of the list to return the list of numbers
>> list = ['1',  '2', '3']
=> ["1", "2", "3"]
>> list.map {|item| item.to_i}
=> [1, 2, 3]

That is, we called the to_i method on each item of the list, thus converting the 3 strings into 3 integers. Of course, we could have called any method on any set of objects.

Advanced Guide to Symbol.to_proc

After doing that a few times, you start wishing there was simpler syntax. Enter: Symbol.to_proc

>> list.map &:to_i
=> [1, 2, 3]

It looks like magic. Well it certainly doesn’t make any sense. But it works. (The secret: the :to_id symbol is cast into a Proc object by the leading &. That is, it calls the to_proc method on the symbol. Rest of explanation here.)

Magical version of Symbol.to_proc

Quite frankly, that’s still a lot of syntax. Plus, I normally forget to added parentheses around the &:to_i, and then latter I want to invoke another method on the result, so I need to add the parentheses which is a pain… anyway. I thought of something niftier and dare I say, more magical.

How about this syntax:

>> list.to_is
=> [1, 2, 3]

This syntax makes sense – to_is is the plural of to_i – its obvious you want the to_i‘s of your list.

What’s happening here?You pass the plural of the method name to the container and it invokes the singular of the method name upon the children using the map code above. Source is below.

More examples? Want to get the names of all the objects of a list? (assuming that each item in the list has a name method)

>> contacts.map {|contact| contact.name}
=> ['Dr Nic', 'Banjo', ...]
>> contacts.map &:name
=> ['Dr Nic', 'Banjo', ...]
>> contacts.names
=> ['Dr Nic', 'Banjo', ...]

You pick your favourite. I love the last one.

Bonus examples:

>> (1..10).to_a.to_ss
=> ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
>> (1..10).to_a.days
=> [86400, 172800, 259200, 345600, 432000, 518400, 604800, 691200, 777600, 864000]
>> [2,'two', :two].classes
=> [Fixnum, String, Symbol]
>> [2,'two', :two].classes.names
=> ["Fixnum", "String", "Symbol"]
>> [2,'two', :two].classes.names.lengths
=> [6, 6, 6]

So much happy syntax in one place!

UPDATE: After conversation on Ruby Forums, we’ve come up with some new syntax:

>> (1..5).to_a.map_days
=> [86400, 172800, 259200, 345600, 432000]
>> list = [nil, 1, 2, nil, 4]
=> [nil, 1, 2, nil, 4]
>> list.reject_nil?
=> [1, 2, 4]

Neat.

How do I do this at home?

Download and include this mini-library. Source below. Have fun.

module GenericMapToProc
  def self.included(base)
    super

    base.module_eval <<-EOS
      def method_missing(method, *args, &block)
        super
      rescue NoMethodError
        error = $!
        begin
          re = /(map|collect|select|each|reject)_([\\\\w\\\\_]+\\\\??)/
          if (match = method.to_s.match(re))
            iterator, callmethod = match[1..2]
            return self.send(iterator) {|item| item.send callmethod}
          end
          return self.map {|item| item.send method.to_s.singularize.to_sym}
        rescue NoMethodError
          nil
        end
        raise error
      end
    EOS
  end
end

unless String.instance_methods.include? "singularize"
  String.module_eval <<- EOS
    def singularize
      self.gsub(/e?s\Z/,'')
    end
  EOS
end

# Add this to the Array class
Array.send :include, GenericMapToProc

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