---------------------
tom.luo$gmail.com
2010/3/6
---------------------
ri to Ruby is what perldoc to Perl.

1. Install ri on Ubuntu
$sudo apt-get install ri

2. View the documentation for a given class
$ri Array

3. View the documentation for a given method

ri 'Array#delete'

----------------------------------------------------------- 
Array#delete
     array.delete(obj)            -> obj or nil 
     array.delete(obj) { block }  -> obj or nil
------------------------------------------------------------------------
     Deletes items from _self_ that are equal to _obj_. If the item is
     not found, returns +nil+. If the optional code block is given,
     returns the result of _block_ if the item is not found.

        a = [ "a", "b", "b", "b", "c" ]
        a.delete("b")                   #=> "b"
        a                               #=> ["a", "c"]
        a.delete("z")                   #=> nil
        a.delete("z") { "not found" }   #=> "not found"


Example:
        a=(1..100).to_a
        a.delete(88) 

============
Arrary permutation
===========

irb(main):012:0> a=(1..3).to_a
=> [1, 2, 3]
irb(main):013:0> a.permutation.to_a
=> [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
irb(main):014:0>

 (1..10).to_a.permutation.to_a.size
=> 3628800

irb(main):014:0> (1..10).to_a.inject(:*)
=> 3628800
10*9*8*7*6*5*4*3*2*1 = 3628800

================
Quotes
===============

You can include double quotes, single quotes and special characters in a BLOCK

s = <<BLOCK
This is a "double quoted string"
This is a 'single quoted string'
\ backslash
/ forward slash
BLOCK


=================
Array
=================
a = (1..10).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
a.inject(:+)
=> 55

a.inject(:*)
=> 3268800

=================
Bignum
=================
n=2**80
1208925819614629174706176
Bit reference returns the nth bit in the binary representation of n. n[0] is the least significant bit.

n[80] = 1
irb(main):033:0> 80.downto(0) do |bit| print n[bit]  end
100000000000000000000000000000000000000000000000000000000000000000000000000000000=> 80

===============
BigDecimal
===============
require 'bigdecimal'
require 'bigdecima/math'
include BigMath
pi = BigMath::PI(30)
=> #<BigDecimal:7f57a0453428,'0.3141592653 5897932384 6264338327 9502884197 1693995304 6425865850 678E1',72(153)>
rb(main):019:0> pi.to_s
=> "0.314159265358979323846264338327950288419716939953046425865850678E1"

===============
Converting number from decimal to hexadecimal, or octal to binary etc base conversion.
===============

Decimal number to hexadecimal

16.to_s(16)

=> "10"

10.to_s(16)

=>"a"

(2^^27).to_s(16)

"33b2e3c9fd0803ce8000000"

"33b2e3c9fd0803ce8000000".to_i(16)
==> 1000000000000000000000000000
Hexadecimal to decimal
"33b2e3c9fd0803ce8000000".to_i(16)    ==> 1000000000000000000000000000

Decimal to binary

1024.to_s(2)

==> "10000000000"

Binary to decimal
"10000000000".to_i(2)
==> 1024

=============
Generate random strings
=============
Math::E.step(Math::PI,0.000001) {|i| print i.to_s.crypt(‘tluo’), " "}


==============
View ri doc in ANSI format
==============
ri --format ansi -T Array.sort

Format is to use when display output:

ansi, bs, html, plain, simple

To use ANSI, either also use the -T option, or tell your pager to allow control characters.


==============
Install MySQL/Ruby on Ubuntu
===============

http://oracleabc.com/ruby/mysql_ruby.txt

==============
Read RSS news in VIM
==============
http://oracleabc.com/ubuntu/read_news_in_vim.txt