class Array

Returns the value after the given value. The value before the last is the first. Returns nil if the given value is not in the array.

Examples

sequence = ['a', 'b', 'c']
sequence.after('a')           #=> 'b'
sequence.after('b')           #=> 'c'
sequence.after('c')           #=> 'a'
sequence.after('d')           #=> nil

CREDIT: Tyler Rick

# File lib/facets/array/before.rb, line 33
def after(value)
  return nil unless include? value
  self[(index(value).to_i + 1) % length]
end

Returns the value previous to the given value. The value previous to the first is the last. Returns nil if the given value is not in the array.

Examples

sequence = ['a', 'b', 'c']
sequence.before('a')           #=> 'c'
sequence.before('b')           #=> 'a'
sequence.before('c')           #=> 'b'
sequence.before('d')           #=> nil

CREDIT: Tyler Rick

# File lib/facets/array/before.rb, line 16
def before(value)
  return nil unless include? value
  self[(index(value).to_i - 1) % length]
end

Simplify an array by flattening it then compacting it.

[1,[2,nil,[3]],nil,4].collapse  #=> [1,2,3,4]

# File lib/facets/array/collapse.rb, line 7
def collapse
  flatten.compact
end

Yields the block to each unique combination of n elements.

a = %w|a b c d|
a.combination(3)

produces

[["a", "b", "c"],
 ["a", "b", "d"],
 ["a", "c", "d"],
 ["b", "c", "d"]]

CREDIT: Florian Gross

# File lib/facets/array/combination.rb, line 21
def combination(k=2)
  if block_given?
    s = to_a
    n = s.size
    return unless (1..n) === k
    idx = (0...k).to_a
    loop do
      yield s.values_at(*idx)
      i = k - 1
      i -= 1 while idx[i] == n - k + i
      break if i < 0
      idx[i] += 1
      (i + 1 ... k).each {|j| idx[j] = idx[i] + j - i}
    end
  else
    to_enum(:combination, k)
  end
end

Returns all items that are equal in terms of the supplied block. If no block is given objects are considered to be equal if they return the same value for Object#hash and if obj1 == obj2.

[1, 2, 2, 3, 4, 4].commonality  #=> { 2 => [2, 2], 4 => [4, 4] }

["foo", "bar", "a"].commonality { |str| str.length }
#=> { 3 => ["foo", "bar"] }

This can be useful, for instance, in determining all persons that share their last name with another person …

persons.collisions { |person| person.last_name }

CREDIT: Florian Gross

# File lib/facets/array/commonality.rb, line 19
def commonality(&block)
  had_no_block = !block
  block ||= lambda { |item| item }
  result = Hash.new { |hash, key| hash[key] = Array.new }
  each do |item|
    key = block.call(item)
    result[key] << item
  end
  result.reject! do |key, values|
    values.size <= 1
  end
  # -- return had_no_block ? result.values.flatten : result
  return result
end

This is more advanced form of join. It allows for fine control of separators.

NOTE: The old version used to default its separator to “, ” and default the terminating separator to “ and ”. This is no longer the case. You must specifically provide these parameters.

If no paramters are given, it acts like join but will a space separator.

[1,2,3].conjoin
#=> "1 2 3"

Use comma+space and 'and' on tail.

[1,2,3].conjoin(', ', ' and ')
#=> "1, 2 and 3"

Use comma+space and 'or' on tail using :last option.

[1,2,3].conjoin(', ', :last => ' or ')
#=> "1, 2 or 3"

Use semicolon+space and ampersand on tail using index.

[1,2,3].conjoin('; ', -1 => ' & ')
#=> "1; 2 & 3"

Can take a block to determine separator.

[1,2,3,4].conjoin{ |i, a, b| i % 2 == 0 ? '.' : '-' }
#=> "1.2-3.4"

This makes very esoteric transformation possible.

[1,1,2,2].conjoin{ |i, a, b| a == b ? '=' : ' != ' }
#=> "1=1 != 2=2"

[1,2,3,4].conjoin{ |i, x, y| "<#{i} #{x} #{y}>" }
#=> "1<0 1 2>2<1 2 3>3<2 3 4>4"

There are also spacing options. Providing the :space option pads the separators.

[1,2,3].conjoin(',', '&', :space=>2)
#=> "1  ,  2  &  3"

And the :spacer option can set an alternate spacing string.

[1,2,3].conjoin('|', '>', :space=>2, :spacer=>'-')
#=> "1--|--2-->--3"

CREDIT: Trans

# File lib/facets/array/conjoin.rb, line 57
def conjoin(*args, &block)
  return first.to_s if size < 2

  options = (Hash===args.last) ? args.pop : {}

  spacing = options.delete(:space)  || 0
  spacer  = options.delete(:spacer) || " "
  space   = spacer * spacing.to_i

  sep = []

  if block_given?
    (size - 1).times do |i|
      sep << space + yield(i, *slice(i,2)) + space
    end
  else
    separator   = args.shift || " "
    options[-1] = args.shift if args.first

    options[0]  = options.delete(:first) if options.key?(:first)
    options[-1] = options.delete(:last)  if options.key?(:last)

    separator = space + separator + space

    sep = [separator] * (size - 1)

    options.each{|i, s| sep[i] = space + s + space}
  end
  zip(sep).join
end

Inverse of delete_if.

[1,2,3].delete_unless{ |x| x < 2 }
#=> [1]

CREDIT: Daniel Schierbeck

# File lib/facets/array/delete_unless.rb, line 10
def delete_unless(&block)
  delete_if { |element| not block.call(element) }
end

Delete multiple values from array.

a = [1,2,3,4]
a.delete_values(1,2)   #=> [1,2]
a                      #=> [3,4]

CREDIT: Trans

# File lib/facets/array/delete_values.rb, line 11
def delete_values(*values)
  d = []
  values.each{ |v| d << delete(v) }
  d
end

Delete multiple values from array given indexes or index range.

a = [1,2,3,4]
a.delete_values_at(1,2)   #=> [2,3]
a                         #=> [1,4]
a = [1,2,3,4]
a.delete_values_at(0..2)  #=> [1,2,3]
a                         #=> [4]

NOTE: It would be nice to see delete_at incorporate this funcitonaility.

CREDIT: Trans

# File lib/facets/array/delete_values.rb, line 32
def delete_values_at(*selectors)
  idx = []
  selectors.each{ |i|
    case i
    when Range
      idx.concat( i.to_a )
    else
      idx << i.to_i
    end
  }
  idx.uniq!
  dvals = values_at(*idx)
  idx = (0...size).to_a - idx
  self.replace( values_at(*idx) )
  return dvals
end

Divide on matching pattern.

['a1','b1','a2','b2'].divide(/^a/)
#=> [['a1','b1'],['a2','b2']]

CREDIT: Trans

# File lib/facets/array/divide.rb, line 10
def divide(pattern)
  memo = []
  each do |obj|
    memo.push [] if pattern === obj
    memo.last << obj
  end
  memo
end

Return list of duplictate elements.

@param [Integer] min

The minimum number of duplicatation necessary for inclusion.

@author Rebort Dober (current implementation) @author Thibaut Barrère

# File lib/facets/array/nonuniq.rb, line 38
def duplicates(min=2)
  h = Hash.new( 0 )
  each {|i|
    h[i] += 1
  }
  h.delete_if{|_,v| v < min}.keys
end

Iterate over index and value. The intention of this method is to provide polymorphism with Hash.

# File lib/facets/array/each_pair.rb, line 6
def each_pair #:yield:
  i = -1
  each_value do |x|
    yield(i+=1, x)
  end
end

Shannon's entropy for an array - returns the average bits per symbol required to encode the array. Lower values mean less “entropy” - i.e. less unique information in the array.

e = %w{ a b c d e e e }.entropy

("%.3f" % e)  #=> "2.128"

CREDIT: Derek

# File lib/facets/array/entropy.rb, line 16
def entropy
  arr = self
  probHash = arr.probability
  # -- h is the Shannon entropy of the array
  h = -1.to_f * probHash.keys.inject(0.to_f) do |sum, i|
    sum + (probHash[i] * (Math.log(probHash[i])/Math.log(2.to_f)))
  end
  h
end

Extracts options from a set of arguments. Removes and returns the last element in the array if it's a hash, otherwise returns a blank hash.

def options(*args)
  args.extract_options!
end

options(1, 2)           # => {}
options(1, 2, :a => :b) # => {:a=>:b}

# File lib/facets/array/extract_options.rb, line 23
def extract_options!
  if Hash === last && last.extractable_options?
    pop
  else
    {}
  end
end

Returns last n elements.

%w{W o r l d}.from(3)  #=> %w{l d}

# File lib/facets/array/from.rb, line 7
def from(i)
  return self if i >= size
  self[i, size - i]
end

Returns the maximum possible Shannon entropy of the array with given size assuming that it is an “order-0” source (each element is selected independently of the next).

CREDIT: Derek

# File lib/facets/array/entropy.rb, line 32
def ideal_entropy
  arr = self
  unitProb = 1.0.to_f / arr.size.to_f
  (-1.to_f * arr.size.to_f * unitProb * Math.log(unitProb)/Math.log(2.to_f))
end

Allows index to accept a block.

['a', 'b', 'c'].index{ |x| x.upcase == 'C' } #=> 2

IMPORTANT: This is one of the few core overrides in Facets.

# File lib/facets/array/index.rb, line 12
def index(obj=nil, &block)
  if block_given?
    _facets_index(find(&block))
  else
    _facets_index(obj)
  end
end

Determines the sorted middle element.

a = %w{a a b b c c c}
a.median     #=> "b"

When there are an even number of elements, the greater of the two middle elements is given.

a = %w{a a b b c c c d}
a.median     #=> "c"

An offset can be supplied to get an element relative to the middle.

a = %w{a a b b c c c d}
a.median(-1) #=> "b"

The the array is empty, nil is returned.

@return [Object] sorted middle element

# File lib/facets/array/median.rb, line 23
def median(offset=0)
  return nil if self.size == 0

  tmp = self.sort
  mid = (tmp.size / 2).to_i + offset

  tmp[mid]
end

In place merge.

a = [1,2]
a.merge! [2,3]
a #=> [1,2,3]

CREDIT: Trans

# File lib/facets/array/merge.rb, line 11
def merge!( other )
  self.replace(self.merge(other))
end

In Statistics mode is the value that occurs most frequently in a given set of data. This method returns an array in case their is a tie.

[:a, :b, :c, :b, :d].mode  #=> [:b]
[:a, :b, :c, :b, :a].mode  #=> [:a, :b]

Returns an Array of most common elements.

@author Robert Klemme

# File lib/facets/array/mode.rb, line 14
def mode
  max = 0
  c = Hash.new 0
  each {|x| cc = c[x] += 1; max = cc if cc > max}
  c.select {|k,v| v == max}.map {|k,v| k}
end

Returns a list of non-unique elements

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

@author Martin DeMello

# File lib/facets/array/nonuniq.rb, line 9
def nonuniq
  h1 = {}
  h2 = {}
  each {|i|
    h2[i] = true if h1[i]
    h1[i] = true
  }
  h2.keys
end

Same as `#nonuniq` but acting in place.

# File lib/facets/array/nonuniq.rb, line 20
def nonuniq!
  h1 = {}
  h2 = {}
  each {|i|
    h2[i] = true if h1[i]
    h1[i] = true
  }
  self.replace(h2.keys)
end

Not empty?

[].not_empty?     #=> false
[1,2].not_empty?  #=> true

# File lib/facets/array/not_empty.rb, line 8
def not_empty?
  !empty?
end

Returns a list of elements that occur n times.

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

If n is a Range then returns elements that occur a number of time within the range.

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

@author Robert Dober

# File lib/facets/array/nonuniq.rb, line 57
def occurent(n=2)
  h = Hash.new( 0 )
  each do |i|
    h[i] += 1
  end

  case n
  when nil
    h.delete_if{ |_,v| ! yield(v) }.keys
  when Range
    h.delete_if{ |_,v| ! n.include?(v) }.keys
  else
    h.delete_if{|_,v| v != n}.keys
  end
end

Returns the only element in the array. Raises an IndexError if the array's size is not 1.

[5].only      # => 5

expect IndexError do
  [1,2,3].only
end

expect IndexError do
  [].only
end

CREDIT: Gavin Sinclair, Noah Gibbs

# File lib/facets/array/only.rb, line 18
def only
  unless size == 1
    raise IndexError, "Array#only called on non-single-element array"
  end
  first
end

Pad an array with a given value up to a given length.

[0,1,2].pad(6,"a")  #=> [0,1,2,"a","a","a"]

If length is a negative number padding will be added to the beginning of the array.

[0,1,2].pad(-6,"a")  #=> ["a","a","a",0,1,2]

CREDIT: Richard Laugesen

# File lib/facets/array/pad.rb, line 14
def pad(len, val=nil)
  return dup if self.size >= len.abs
  if len < 0
    Array.new((len+size).abs,val) + self
  else
    self + Array.new(len-size,val)
  end
end

Like pad but changes the array in place.

a = [0,1,2]
a.pad!(6,"x")
a  #=> [0,1,2,"x","x","x"]

CREDIT: Richard Laugesen

# File lib/facets/array/pad.rb, line 31
def pad!(len, val=nil)
  return self if self.size >= len.abs
  if len < 0
    replace Array.new((len+size).abs,val) + self
  else
    concat Array.new(len-size,val)
  end
end

Peek at the top of the stack (the end of the array).

a = [1, 2, 3]
a.peek          #=> 3
a               #=> [1, 2, 3]

Or provide an index to inspect the array from back to front.

# File lib/facets/array/pull.rb, line 14
def peek(i=0)
  i = -(i + 1)
  fetch(i)
end

Permutation provids the possible orders of an enumerable. Each is indexed by a permutation number. The maximum number of arrangements is the factorial of the size of the array.

[1,2].permutation(2).to_a #=> [[1,2], [2,1]]

CREDIT: Shin-ichiro Hara

# File lib/facets/array/permutation.rb, line 13
def permutation(n=size)
  if size < n or n < 0
  elsif n == 0
    yield([])
  else
    self[1..-1].permutation(n - 1) do |x|
      (0...n).each do |i|
        yield(x[0...i] + [first] + x[i..-1])
      end
    end
    self[1..-1].permutation(n) do |x|
      yield(x)
    end
  end
end

Put an object on the bottom of the stack (front of the array).

a = [2, 3]
a.poke(1)
a               #=> [1, 2, 3]

Or supply an index and poke works like insert.

# File lib/facets/array/pull.rb, line 26
def poke(x, i=0)
  insert(i,x)
end

Generates a hash mapping each unique element in the array to the relative frequency, i.e. the probablity, of it appearence.

[:a, :b, :c, :c].probability  #=> {:a=> 0.25, :b=>0.25, :c=>0.5}

CREDIT: Brian Schröder

# File lib/facets/array/probability.rb, line 10
def probability
  probs = Hash.new(0.0)
  size = 0.0
  each do |e|
    probs[e] += 1.0
    size += 1.0
  end
  probs.keys.each{ |e| probs[e] /= size }
  probs
end

Provides the cartesian product of two or more arrays.

a = [1,2].product([4,5])
a  #=> [[1, 4],[1, 5],[2, 4],[2, 5]]

CREDIT: Thomas Hafner

# File lib/facets/array/product.rb, line 12
def product(*enums)
  enums.unshift self
  result = [[]]
  while [] != enums
    t, result = result, []
    b, *enums = enums
    t.each do |a|
      b.each do |n|
        result << a + [n]
      end
    end
  end
  result
end

Apply a block to array, and recursively apply that block to each sub-array or types.

arr = ["a", ["b", "c", nil], nil]
arr.recurse{ |a| a.compact! }
#=> ["a", ["b", "c"]]

# File lib/facets/array/recurse.rb, line 10
def recurse(*types, &block)
  types = [self.class] if types.empty?
  a = inject([]) do |array, value|
    case value
    when *types
      array << value.recurse(*types, &block)
    else
      array << value
    end
    array
  end
  yield a
end

In place form of recurse.

# File lib/facets/array/recurse.rb, line 25
def recurse!(&block)
  replace(recurse(&block))
end

Apply a method to array, and recursively apply that method to each sub-array or types.

arr = ["a", ["b", "c"]]
arr.recursively.map{ |v| v.to_sym }
#=> [:a, [:b, :c]]

By default the sub-types are passed thru uneffected. Passing a block to recursively changes this.

arr = ["a", ["b", "c"]]
arr.recursively{ |a| a.reverse }.map{ |v| v.to_sym }
#=> [:a, [:c, :b]]

TODO: Return Enumerator if no yld block is given ?

# File lib/facets/array/recursively.rb, line 21
def recursively(*types, &block)
  Recursor.new(self, *types, &block)
end

Rotates an array's elements from back to front n times.

[1,2,3].rotate      #=> [2,3,1]
[2,3,1].rotate      #=> [3,1,2]
[3,1,2].rotate      #=> [1,2,3]

[1,2,3].rotate(3)   #=> [1,2,3]

A negative parameter reverses the order from front to back.

[1,2,3].rotate(-1)  #=> [3,1,2]

CREDIT: Florian Gross, Thomas Sawyer

# File lib/facets/array/rotate.rb, line 19
def rotate(n=1)
  self.dup.rotate!(n)
end

Same as rotate, but acts in place.

a = [1,2,3]
a.rotate!
a  #=> [2,3,1]

CREDIT: Florian Gross, Thomas Sawyer

# File lib/facets/array/rotate.rb, line 35
def rotate!(n=1)
  n = n.to_int
  return self if (n == 0 or self.empty?)
  if n < 0
    n.abs.times{ self.unshift( self.pop ) }
  else
    n.abs.times{ self.push( self.shift ) }
  end
  self
end

As with select but modifies the Array in place.

a = [1,2,3,4,5,6,7,8,9,10]
a.select!{ |e| e % 2 == 0 }
a  #=> [2,4,6,8,10]

CREDIT: Gavin Sinclair

# File lib/facets/array/select.rb, line 13
def select!  # :yield:
  reject!{ |e| not yield(e) }
end

Splice acts a combination of slice! and store. If two arguments are given it calls store. If a single argument is given it calls slice!.

a = [1,2,3]
a.splice(1)    #=> 2
a              #=> [1,3]

a = [1,2,3]
a.splice(1,4)  #=> 4
a              #=>[1,4,3]

CREDIT: Trans

# File lib/facets/array/splice.rb, line 19
def splice(*args)
  if args.size == 1
    slice!(*args)
  else
    store(*args)
  end
end

Split on matching pattern. Unlike divide this does not include matching elements.

['a1','a2','b1','a3','b2','a4'].split(/^b/)
#=> [['a1','a2'],['a3'],['a4']]

CREDIT: Trans

# File lib/facets/array/split.rb, line 10
def split(pattern)
  memo = []
  sect = []
  each do |obj|
    if pattern === obj
      memo << sect
      sect = []
    else
      sect << obj
    end
  end
  memo << sect
  memo.pop while memo.last == []
  memo
end

Fetch values from a start index thru 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/facets/array/from.rb, line 20
def thru(from, to=nil)
  from, to = 0, from unless to
  to = size - 1 if to >= size
  a = []
  i = from
  while i <= to
    a << self[i]
    i += 1
  end
  a
end

Boolean conversion for not empty?

# File lib/facets/boolean.rb, line 110
def to_b
  ! self.empty?
end

Converts an array into a hash. Converting an array into a hash is not a one-to-one conversion, for this reason to_h examines at the array being converted and then dispatches the conversion to the most sutiable specialized function. There are three possiblities for this.

If the array is a collection of perfect pairs, like that which Hash#to_a generates, then conversion is handled by to_h_flat.

a = [ [:a,1], [:b,2] ]
a.to_h  #=> { :a=>1, :b=>2 }

If the array contains only arrays, but are not perfect pairs, then to_h_multi is called.

a = [ [:a,1,2], [:b,2], [:c], [:d] ]
a.to_h  #=> { :a=>[1,2], :b=>[2], :c=>[], :d=>[] }

If the array contians objects other then arrays then the to_h_splat method is called.

a = [ [:a,1,2], 2, :b, [:c,3], 9 ]
a.to_h  #=> { [:a,1,2]=>2, :b=>[:c,3], 9=>nil }

Finally, a particular dispatch can be forced by specifying the mode of conversion, eg. :multi, :splat, :flat, :assoc, etc.

Setting mode to true is the same as setting it :multi. This has been left in for backward compatability.

NOTE: The use of a values parameter has been deprecated because that functionality is as simple as …

array1.zip(array2).to_h

CREDIT: Robert Klemme, Trans

# File lib/facets/to_hash.rb, line 51
def to_h(mode=nil)
  case mode
  when :splat
    return to_h_splat
  when :flat
    return to_h_flat
  when :multi, true
    return to_h_multi
  when :assoc
    return to_h_assoc
  else
    return to_h_auto
  end
end

When a mixed or multi-element accociative array is used, the result is as follows:

a = [ [:a,1,2], [:b,2], [:c], :d ]
a.to_h  #=> { :a=>[1,2], :b=>[2], :c=>[], :d=>[] }

If the first entry of any subelements are the same, then the value will be set to the last occuring value.

a = [ :x, [:x], [:x,1,2], [:x,3], [:x,4] ]
a.to_h_assoc  #=> { :x=>[4] }

# File lib/facets/to_hash.rb, line 157
def to_h_assoc
  h = {}
  each do |k,*v| 
    h[k] = v
  end
  h
end

Converts an array into a hash. Converting an array into a hash is not a one-to-one conversion, for this reason to_h examines at the array being converted and then dispatches the conversion to the most sutiable specialized function. There are three possiblities for this.

If the array is a collection of perfect pairs, like that which Hash#to_a generates, then conversion is handled by to_h_flat.

a = [ [:a,1], [:b,2] ]
a.to_h_auto  #=> { :a=>1, :b=>2 }

If the array contains only arrays, but are not perfect pairs, then to_h_multi is called.

a = [ [:a,1,2], [:b,2], [:c], [:d] ]
a.to_h_auto  #=> { :a=>[1,2], :b=>[2], :c=>[], :d=>[] }

If the array contians objects other then arrays then the to_h_splat method is called.

a = [ [:a,1,2], 2, :b, [:c,3], 9 ]
a.to_h_auto  #=> { [:a,1,2]=>2, :b=>[:c,3], 9=>nil }

# File lib/facets/to_hash.rb, line 91
def to_h_auto
  pairs = true
  mixed = false

  each do |e|
    case e
    when Array
      pairs = false if e.size > 2
    else
      mixed = true
    end
  end

  if mixed
    to_h_splat
  elsif pairs
    to_h_flat
  else
    to_h_multi
  end
end

This is equivalent to Hash, but it will pad the array with a nil object if there are not an even number of elements.

a = [:a,1,[:b,2,:c]]
a.to_h_flat  #=> { :a=>1, :b=>2, :c=>nil }

# File lib/facets/to_hash.rb, line 133
def to_h_flat
  a = flatten
  a << nil if a.size % 2 == 1
  Hash[*a]
end

When a mixed or multi-element accociative array is used, the result is as follows:

a = [ [:a,1,2], [:b,2], [:c], :d ]
a.to_h  #=> { :a=>[1,2], :b=>[2], :c=>[], :d=>[] }

If the first entry of the subelements is the same, then the values will be merged using concat.

a = [ [:a,1,2], [:a,3], [:a,4], [:a], :a ]
a.to_h_multi  #=> { :a=>[1,2,3,4] }

# File lib/facets/to_hash.rb, line 177
def to_h_multi
  h = {}
  each do |k,*v| 
    h[k] ||= []
    h[k].concat(v)
  end
  h
end

This is equivalent to Hash, but it will pad the array with a nil object if there are not an even number of elements.

a = [:a,1,:b,2,:c]
a.to_h_splat  #=> { :a=>1, :b=>2, :c=>nil }

# File lib/facets/to_hash.rb, line 120
def to_h_splat
  a = dup
  a << nil if a.size % 2 == 1
  Hash[*a]
end

Returns a new array created by traversing the array and its sub-arrays, executing the given block on the elements.

h = ["A", "B", ["X", "Y"]]

g = h.traverse{ |e| e.downcase }

g  #=> ["a", "b", ["x", "y"]]

This is the same as recursive.map and will likely be deprecated in the future because of it.

CREDIT: Trans

# File lib/facets/array/traverse.rb, line 16
def traverse(&block)
  if block_given?
    map do |e|
      if e.respond_to?(:to_ary)
        e.to_ary.traverse(&block)
      else
        block.call(e)
      end
    end
  else
    to_enum(:traverse)
  end
end

Like recursive_map, but will change the array in place.

h = ["A", "B", ["X", "Y"]]

h.traverse!{ |e| e.downcase }

h  #=> ["a", "b", ["x", "y"]]

CREDIT: Trans

# File lib/facets/array/traverse.rb, line 39
def traverse!(&block)
  replace(traverse(&block))
end

Like uniq, but determines uniqueness based on a given block.

a = (-5..5).to_a
a.uniq_by!{ |i| i*i }
a #=> [-5, -4, -3, -2, -1, 0]

As can be seen in the example, order is significant.

# File lib/facets/array/uniq_by.rb, line 10
def uniq_by! #:yield:
  h = {}
  replace( inject([]){|a,x| h[yield(x)] ||= a << x} )
end