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More Ruby Tips and Tricks

String to number conversion gotcha

>> Float('3.14159')
=> 3.14159 
>> '3.14159'.to_f
=> 3.14159 

# However, Float() method will return an exception if given
# a bad input while to_f() will ignore everything from the 
# offending character.

>> Float('3.x14159')
ArgumentError: invalid value for Float(): "3.x14159"
  from (irb):4:in 'Float'
  from (irb):4

>> '3.x14159'.to_f
=> 3.0


# Similar case with to_i() and Integer().

>> Integer('19x69')
ArgumentError: invalid value for Integer(): "19x69"
  from (irb):15:in 'Integer'
  from (irb):15
  from /Users/greg/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in '<main>'

>> '19x69'.to_i
=> 19

Case insensitive regular expression

# Regex is case sensitive by default.
# Adding 'i' for insensitive match
puts 'matches' if  /AM/i =~ 'am'

Hash is ordered in 1.9

# new syntax in 1.9
h = {first: 'a', second: 'b', third: 'c'}

# hashes in 1.9 are ordered
h.each do |e|
  pp e
end

Filter a list using several conditions

conditions = [
    proc { |i| i > 5 },
    proc { |i| (i % 2).zero? },
    proc { |i| (i % 3).zero? }
  ]

matches = (1..100).select do |i|
  conditions.all? { |c| c[i] }
end

Randomly pick an element from an array

>> [1,2,3,4,5].sample
=> 2 
>> [1,2,3,4,5].sample
=> 1 

# pick 2 random elements
>> [1,2,3,4,5].sample(2)
=> [1, 5]

List methods unique to a class

# List all instance methods that starts with `re` including those inherited by String.

>> String.instance_methods.grep /^re/
=> [:replace, :reverse, :reverse!, :respond_to?, :respond_to_missing?] 

# List methods unique to String, i.e. not include
# those defined by its ancestors.

>> String.instance_methods(false).grep /^re/
=> [:replace, :reverse, :reverse!]

Globbing key-value pairs

>> h = Hash['a', 1, 'b', 2]
=> {"a"=>1, "b"=>2}

>> h = Hash[ [ ['a', 1], ['b', 2] ] ] 
=> {"a"=>1, "b"=>2}

>> h = Hash[ 'a' => 1, 'b' => 2 ]
=> {"a"=>1, "b"=>2}

# The first form is very useful for globbing key-value pairs in Rails’ routes. For example, if you have the following:

# route definition in Rails 3
match 'items/*specs' => 'items#specs'

# sample url
http://localhost:3000/items/year/1969/month/7/day/21

# params[:specs] will be set

>> params[:specs]
=> "year/1969/month/7/day/21"

>> h = Hash[*params[:specs].split('/')]
=> {"year"=>"1969", "month"=>"7", "day"=>"21"}
03 Mar 2012