Class: Interval

Inherits:
Object show all
Includes:
Enumerable::Arguments, Multiton
Defined in:
lib/supplemental/facets/interval.rb

Overview

Interval

While Ruby support the Range class out of the box, is does not quite fullfil the role od a real Interval class. For instance, it does not support excluding the front sentinel. This is because Range also tries to do triple duty as a simple Sequence and as a simple Tuple-Pair, thus limiting its potential as an Interval. The Interval class remedies the situation by commiting to interval behavior, and then extends the class’ capabilites beyond that of the standard Range in ways that naturally fall out of that.

Range depends on two methods: #succ and #<=>. If numeric ranges were the only concern, those could just as well be #+ and #<=>, but esoteric forms make that unfeasible –the obvious example being a String range. But a proper Interval class requires mathematical continuation, thus the Interval depends on #+ and #<=>, as well as #- as the inverse of #+.

i = Interval.new(1,5)
i.to_a       #=> [1,2,3,4,5]

i = Interval[0,5]
i.to_a(2)    #=> [0,2,4]

i = Interval[1,5]
i.to_a(-1)   #=> [5,4,3,2,1]

i = Interval[1,3]
i.to_a(1,2)  #=> [1.0,1.5,2.0,2.5,3.0]

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Enumerable::Arguments

#find, #to_a, wrap_enumerable_method

Methods included from Multiton

#clone, #dup

Constructor Details

#initialize(first, last, exclude_first = false, exclude_last = false) ⇒ Interval

Returns a new instance of Interval.

Raises:

  • (ArgumentError) 


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# File 'lib/supplemental/facets/interval.rb', line 95

def initialize(first, last, exclude_first=false, exclude_last=false )
  raise ArgumentError, "bad value for interval" if first.class != last.class
  @first = first
  @last = last
  @exclude_first = exclude_first
  @exclude_last = exclude_last
  @direction = (@last <=> @first)
end

Class Method Details

.[](*args) ⇒ Object 



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# File 'lib/supplemental/facets/interval.rb', line 90

def self.[]( *args )
  self.new( *args )
end

Instance Method Details

#+@ ⇒ Object

Unary shorthands. These return a new interval exclusive of first, last or both sentinels, repectively.



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# File 'lib/supplemental/facets/interval.rb', line 161

def +@ ; Interval.new(first, last, true, false) ; end

#-@ ⇒ Object 



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# File 'lib/supplemental/facets/interval.rb', line 162

def -@ ; Interval.new(first, last, false, true) ; end

#closed ⇒ Object

Returns a new interval inclusive of of both sentinels.



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# File 'lib/supplemental/facets/interval.rb', line 141

def closed; Interval.new(@first, @last, true, true) ; end

#degenerate? ⇒ Boolean

Returns true if the start and end sentinels are equal and the interval is closed; otherwise false.

Returns:

  • (Boolean) 


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# File 'lib/supplemental/facets/interval.rb', line 127

def degenerate? ; @direction == 0 and ! (@exclusive_first or @exclusive_last) ;  end

#direction ⇒ Object

Returns the direction of the interval indicated by +1, 0 or -1.

(1..5).direction  #=> 1
(5..1).direction  #=> -1
(1..1).direction  #=> 0



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# File 'lib/supplemental/facets/interval.rb', line 138

def direction ; @direction ; end

#distance ⇒ Object Also known as: length, size

Returns the length of the interval as the difference between the first and last elements. Returns nil if the sentinal objects do not support distance comparison (#distance). TODO: Add n parameter to count segmentations like those produced by #each.



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# File 'lib/supplemental/facets/interval.rb', line 177

def distance
  @last - @first
  #if @last.respond_to?( :distance )
  #  @last.distance( @first )
  #else
  #  #self.to_a.length
  #end
end

#each(n = 1, d = nil) ⇒ Object Also known as: step

Iterates over the interval, passing each _n_th element to the block. If n is not given then n defaults to 1. Each _n_th step is determined by invoking + or \- n, depending on the direction of the interval. If n is negative the iteration is preformed in reverse form end sentinal to front sentinal. A second parameter, d, can be given in which case the applied step is calculated as a fraction of the interval’s length times n / d. This allows iteration over the whole interval in equal sized segments.

1..5.each { |e| ... }        #=> 1 2 3 4 5
1..5.each(2) { |e| ... }     #=> 1 3 5
1..5.each(1,2) { |e| ... }   #=> 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0



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# File 'lib/supplemental/facets/interval.rb', line 241

def each(n=1, d=nil)  # :yield:
  return (n < 0 ? @last : @first) if degenerate?  # is this right for all values of n ?
  s = d ? self.length.to_f * (n.to_f / d.to_f) : n.abs
  raise "Cannot iterate over zero length steps." if s == 0
  s = s * @direction
  if n < 0
    e = @exclude_last ? @last - s : @last
    #e = @exclude_last ? @last.pred(s) : @last
    t = @exclude_last ? 1 : 0
    #while e.cmp(@first) >= t
    while (e <=> @first) >= t
      yield(e)
      e -= s
      #e = e.pred(s)
    end
  else
    e = @exclude_first ? @first + s : @first
    #e = @exclude_first ? @first.succ(s) : @first
    t = @exclude_last ? -1 : 0
    #while e.cmp(@last) <= t
    while (e <=> @last) <= t
      yield(e)
      e += s
      #e = e.succ(s)
    end
  end
end

#eql?(other) ⇒ Boolean

Compares two intervals to see if they are equal

Returns:

  • (Boolean) 


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# File 'lib/supplemental/facets/interval.rb', line 276

def eql?(other)
  return false unless @first == other.first
  return false unless @last == other.last
  return false unless @exclude_first == other.exclude_first?
  return false unless @exclude_last == other.exclude_last?
  true
end

#exclude_first? ⇒ Boolean Also known as: exclude_begin?

Returns:

  • (Boolean) 


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# File 'lib/supplemental/facets/interval.rb', line 117

def exclude_first? ; @exclude_first ; end

#exclude_last? ⇒ Boolean Also known as: exclude_end?

Returns:

  • (Boolean) 


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# File 'lib/supplemental/facets/interval.rb', line 118

def exclude_last? ; @exclude_last ; end

#first ⇒ Object Also known as: begin

Returns the first or last sentinal of the interval.



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# File 'lib/supplemental/facets/interval.rb', line 113

def first ; @first ; end

#first_closed ⇒ Object

Returns a new interval with one of the two sentinels opened or closed



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# File 'lib/supplemental/facets/interval.rb', line 154

def first_closed ; Interval.new(@first, @last, false, true) ; end

#first_opened ⇒ Object 



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# File 'lib/supplemental/facets/interval.rb', line 156

def first_opened ; Interval.new(@first, @last, true, false) ; end

#half_closed(e = false) ⇒ Object

Returns a new interval with either the first or the last sentinel exclusive. If the parameter is false, the deafult, then the first sentinel is excluded; if the parameter is true, the last sentinel is excluded.



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# File 'lib/supplemental/facets/interval.rb', line 149

def half_closed(e=false)
  e ? Interval.new(@first, @last, true, false) : Interval.new(@first, @last, false, true)
end

#include?(x) ⇒ Boolean Also known as: ===, member?

Returns true or false if the element is part of the interval.

Returns:

  • (Boolean) 


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# File 'lib/supplemental/facets/interval.rb', line 199

def include?(x)
  # todo: infinity?
  tf = exclude_first? ? 1 : 0
  tl = exclude_last? ? -1 : 0
  (x <=> first) >= tf and (x <=> last) <= tl
end

#last ⇒ Object Also known as: end 



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# File 'lib/supplemental/facets/interval.rb', line 114

def last ; @last ; end

#last_closed ⇒ Object 



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# File 'lib/supplemental/facets/interval.rb', line 155

def last_closed ; Interval.new(@first, @last, true, false) ; end

#last_opened ⇒ Object 



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# File 'lib/supplemental/facets/interval.rb', line 157

def last_opened ; Interval.new(@first, @last, false, true) ; end

#max ⇒ Object

Returns the greater of the first and last sentinals.



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# File 'lib/supplemental/facets/interval.rb', line 194

def max
  ((@first <=> @last) == 1) ? @first : @last
end

#min ⇒ Object

Returns the lesser of the first and last sentinals.



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# File 'lib/supplemental/facets/interval.rb', line 189

def min
  ((@first <=> @last) == -1) ? @first : @last
end

#null? ⇒ Boolean

Returns true if the start and end sentinels are equal and the interval is open; otherwise false.

Returns:

  • (Boolean) 


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# File 'lib/supplemental/facets/interval.rb', line 130

def null? ; @direction == 0 and @exclusive_first and @exclusive_last ; end

#opened ⇒ Object

Returns a new interval exclusive of both sentinels.



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# File 'lib/supplemental/facets/interval.rb', line 144

def opened; Interval.new(@first, @last, true, true) ; end

#reversed ⇒ Object

Returns a new interval with the sentinels reversed.

(0..10).reversed  #=> 10..0



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# File 'lib/supplemental/facets/interval.rb', line 169

def reversed
  Interval.new(@last, @first, true, true)
end

#sentinels ⇒ Object

Returns a two element array of first and last sentinels.

(0..10).sentinels   #=> [0,10]



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# File 'lib/supplemental/facets/interval.rb', line 108

def sentinels
  return [@first, @last]
end

#~@ ⇒ Object 



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# File 'lib/supplemental/facets/interval.rb', line 163

def ~@ ; Interval.new(first, last, true, true) ; end