module Indexable

Indexable is a mixin that provides index based methods, working solely with four methods: index, slice, splice and size.

These methods work in harmony. Where index returns a position of a given element, slice returns elements for given positions. splice is like slice but replaces the given position with new values. This method is not part of ruby core, but it generally just an alias for []=, just as slice is an alias of []. size of course simply returns the total length of the indexable object.

NOTE: To test the following methods Indexable needs to be included into Array and array must have splice defined.

require 'facets/array/splice'

class ::Array
  include Indexable
end

CREDIT: Thomas Sawyer

Public Instance Methods

body() click to toggle source

Returns an array of the first element up to, but not including, the last element.

[1,2,3].body  #=> [1,2]
# File lib/core/facets/indexable.rb, line 61
def body
  slice(0,size-1)
end
ends() click to toggle source

A shorting of “ends at”, returns the last index of the indexable object. Returns nil if there are no elements.

[1,2,3,4,5].ends  #=> 4

This nearly equivalent to +size - 1+.

# File lib/core/facets/indexable.rb, line 210
def ends
  return nil if size == 0
  size - 1
end
first(n=1) click to toggle source

Returns first n elements.

%w{H e l l o}.first(3)  #=> %w{H e l}
# File lib/core/facets/indexable.rb, line 148
def first(n=1)
  slice(0, n.to_i)
end
first!() click to toggle source

Remove and return the first element.

a = [1,2,3]
a.first!      #=> 1
a             #=> [2,3]
# File lib/core/facets/indexable.rb, line 188
def first!
  splice(0)
end
first=(x) click to toggle source

Change the first element.

a = ["a","y","z"]
a.first = "x"
a           #=> ["x","y","z"]
# File lib/core/facets/indexable.rb, line 168
def first=(x)
  splice(0,x)
end
foot() click to toggle source

Like last, returning the last element in an array.

[1,2,3].foot  #=> [3]
# File lib/core/facets/indexable.rb, line 48
def foot
  slice(-1,1)
end
from(i) click to toggle source

Returns last n elements.

%w{W o r l d}.from(3)  #=> %w{l d}
# File lib/core/facets/indexable.rb, line 130
def from(i)
  return [] if i >= size
  slice(i, size - i) #slice(-n..-1)
end
head() click to toggle source

Like first but returns the first element in a new array.

[1,2,3].head  #=> [1]
# File lib/core/facets/indexable.rb, line 31
def head
  slice(0,1)
end
index(obj=nil) { |slice(i)| ... } click to toggle source

Returns the index of the first element equal to the given object or satisfying the block condition.

[1,2,3,4].index{ |e| e == 3 }  #=> 2
[1,2,3,4].index{ |e| e > 3 }   #=> 3
# File lib/core/facets/indexable.rb, line 235
def index(obj=nil, &block)
  if block_given?
    size.times do |i|
      return i if yield(slice(i))
    end
  else
    size.times do |i|
      return i if obj == slice(i)
    end
  end
  nil
end
Also aliased as: index_of
index_of(obj=nil, &block)

to be deprecated

Alias for: index
last(n=1) click to toggle source

Returns last n elements.

%w{H e l l o}.last(3)  #=> %w{l l o}
# File lib/core/facets/indexable.rb, line 156
def last(n=1)
  n = n.to_i
  return self if n > size
  slice(-n, n) #slice(-n..-1)
end
last!() click to toggle source

Remove and return the last element.

a = [1,2,3]
a.last!       #=> 3
a             #=> [1,2]
# File lib/core/facets/indexable.rb, line 198
def last!
  splice(-1)
end
last=(x) click to toggle source

Change the last element.

a = [1,2,5]
a.last = 3
a           #=> [1,2,3]
# File lib/core/facets/indexable.rb, line 178
def last=(x)
  splice(-1,x)
end
mid(offset=0) click to toggle source

Returns the middle element of an array, or the element offset from middle if the parameter is given. Even-sized arrays, not having an exact middle, return the middle-right element.

[1,2,3,4,5].mid        #=> 3
[1,2,3,4,5,6].mid      #=> 4
[1,2,3,4,5,6].mid(-1)  #=> 3
[1,2,3,4,5,6].mid(-2)  #=> 2
[1,2,3,4,5,6].mid(1)   #=> 5

In other words, If there are an even number of elements the higher-indexed of the two center elements is indexed as origin (0).

# File lib/core/facets/indexable.rb, line 79
def mid(offset=0)
  slice((size / 2) + offset)
end
middle(birth=0) click to toggle source

Returns an Array of the middle element(s) of an array. Even-sized arrays, not having an exact middle, return a two-element array of the two middle elements.

[1,2,3,4,5].middle        #=> [3]
[1,2,3,4,5,6].middle      #=> [3,4]

A birth can be give to widen the middle on either side.

[1,2,3,4,5].middle(1)   #=> [2,3,4]
[1,2,3,4,5,6].middle(1)   #=> [2,3,4,5]

In contrast to mid which utilizes an offset.

# File lib/core/facets/indexable.rb, line 97
def middle(birth=0)
  i = size / 2 - birth
  if size % 2 == 0
    slice(i - 1, 2 + (2 * birth))
  else
    slice(i, 1 + (2 * birth))
  end
end
pos(i) click to toggle source

Returns the positive ordinal index given a cardinal position, 1 to n or -n to -1.

[1,2,3,4,5].pos(1)   #=> 0
[1,2,3,4,5].pos(-1)  #=> 4
# File lib/core/facets/indexable.rb, line 221
def pos(i)
  if i > 0
    return i - 1
  else
    size + i
  end
end
range(a=nil,z=-1) click to toggle source

Returns the index range between two elements. If no elements are given, returns the range from first to last.

['a','b','c','d'].range            #=> (0..3)
['a','b','c','d'].range('b','d')   #=> (1..3)
# File lib/core/facets/indexable.rb, line 259
def range(a=nil,z=-1)
  if a
    index(a)..index(z)
  else
    (0..(size-1))
  end
end
tail() click to toggle source

Returns an array from second element to last element.

[1,2,3].tail  #=> [2,3]
# File lib/core/facets/indexable.rb, line 39
def tail
  slice(1,length-1)
end
thru(from, to=nil) click to toggle source

Fetch values from a start index through an end index.

[1,2,3,4,5].thru(0,2)  #=> [1,2,3]
[1,2,3,4,5].thru(2,4)  #=> [3,4,5]

[1,2,3,4,5].thru(2)  #=> [1,2,3]
[1,2,3,4,5].thru(4)  #=> [1,2,3,4,5]
# File lib/core/facets/indexable.rb, line 114
def thru(from, to=nil)
  from, to = 0, from unless to
  to = size - 1 if to >= size
  a = []
  i = from
  while i <= to
    a << slice(i)
    i += 1
  end
  a
end