Returns a new array populated with the given objects.

  Array.[]( 1, 'a', /^A/ )
  Array[ 1, 'a', /^A/ ]
  [ 1, 'a', /^A/ ]

Returns a new array. In the first form, the new array is empty. In the second it is created with size copies of obj (that is, size references to the same obj). The third form creates a copy of the array passed as a parameter (the array is generated by calling to_ary on the parameter). In the last form, an array of the given size is created. Each element in this array is calculated by passing the element‘s index to the given block and storing the return value.

   Array.new
   Array.new(2)
   Array.new(5, "A")

   # only one copy of the object is created
   a = Array.new(2, Hash.new)
   a[0]['cat'] = 'feline'
   a
   a[1]['cat'] = 'Felix'
   a

   # here multiple copies are created
   a = Array.new(2) { Hash.new }
   a[0]['cat'] = 'feline'
   a

   squares = Array.new(5) {|i| i*i}
   squares

   copy = Array.new(squares)

Try to convert obj into an array, using to_ary method. Returns converted array or nil if obj cannot be converted for any reason. This method is to check if an argument is an array.

   Array.try_convert([1])   # => [1]
   Array.try_convert("1")   # => nil

   if tmp = Array.try_convert(arg)
     # the argument is an array
   elsif tmp = String.try_convert(arg)
     # the argument is a string
   end

Set Intersection—Returns a new array containing elements common to the two arrays, with no duplicates.

   [ 1, 1, 3, 5 ] & [ 1, 2, 3 ]   #=> [ 1, 3 ]

Repetition—With a String argument, equivalent to self.join(str). Otherwise, returns a new array built by concatenating the int copies of self.

   [ 1, 2, 3 ] * 3    #=> [ 1, 2, 3, 1, 2, 3, 1, 2, 3 ]
   [ 1, 2, 3 ] * ","  #=> "1,2,3"

Concatenation—Returns a new array built by concatenating the two arrays together to produce a third array.

   [ 1, 2, 3 ] + [ 4, 5 ]    #=> [ 1, 2, 3, 4, 5 ]

Array Difference—Returns a new array that is a copy of the original array, removing any items that also appear in other_array. (If you need set-like behavior, see the library class Set.)

   [ 1, 1, 2, 2, 3, 3, 4, 5 ] - [ 1, 2, 4 ]  #=>  [ 3, 3, 5 ]

Append—Pushes the given object on to the end of this array. This expression returns the array itself, so several appends may be chained together.

   [ 1, 2 ] << "c" << "d" << [ 3, 4 ]
           #=>  [ 1, 2, "c", "d", [ 3, 4 ] ]

Comparison—Returns an integer (-1, 0, or +1) if this array is less than, equal to, or greater than other_array. Each object in each array is compared (using <=>). If any value isn‘t equal, then that inequality is the return value. If all the values found are equal, then the return is based on a comparison of the array lengths. Thus, two arrays are ``equal’’ according to Array#<=> if and only if they have the same length and the value of each element is equal to the value of the corresponding element in the other array.

   [ "a", "a", "c" ]    <=> [ "a", "b", "c" ]   #=> -1
   [ 1, 2, 3, 4, 5, 6 ] <=> [ 1, 2 ]            #=> +1

Equality—Two arrays are equal if they contain the same number of elements and if each element is equal to (according to Object.==) the corresponding element in the other array.

   [ "a", "c" ]    == [ "a", "c", 7 ]     #=> false
   [ "a", "c", 7 ] == [ "a", "c", 7 ]     #=> true
   [ "a", "c", 7 ] == [ "a", "d", "f" ]   #=> false

Element Reference—Returns the element at index, or returns a subarray starting at start and continuing for length elements, or returns a subarray specified by range. Negative indices count backward from the end of the array (-1 is the last element). Returns nil if the index (or starting index) are out of range.

   a = [ "a", "b", "c", "d", "e" ]
   a[2] +  a[0] + a[1]    #=> "cab"
   a[6]                   #=> nil
   a[1, 2]                #=> [ "b", "c" ]
   a[1..3]                #=> [ "b", "c", "d" ]
   a[4..7]                #=> [ "e" ]
   a[6..10]               #=> nil
   a[-3, 3]               #=> [ "c", "d", "e" ]
   # special cases
   a[5]                   #=> nil
   a[5, 1]                #=> []
   a[5..10]               #=> []

Element Assignment—Sets the element at index, or replaces a subarray starting at start and continuing for length elements, or replaces a subarray specified by range. If indices are greater than the current capacity of the array, the array grows automatically. A negative indices will count backward from the end of the array. Inserts elements if length is zero. An IndexError is raised if a negative index points past the beginning of the array. See also Array#push, and Array#unshift.

   a = Array.new
   a[4] = "4";                 #=> [nil, nil, nil, nil, "4"]
   a[0, 3] = [ 'a', 'b', 'c' ] #=> ["a", "b", "c", nil, "4"]
   a[1..2] = [ 1, 2 ]          #=> ["a", 1, 2, nil, "4"]
   a[0, 2] = "?"               #=> ["?", 2, nil, "4"]
   a[0..2] = "A"               #=> ["A", "4"]
   a[-1]   = "Z"               #=> ["A", "Z"]
   a[1..-1] = nil              #=> ["A", nil]
   a[1..-1] = []               #=> ["A"]

Searches through an array whose elements are also arrays comparing obj with the first element of each contained array using obj.==. Returns the first contained array that matches (that is, the first associated array), or nil if no match is found. See also Array#rassoc.

   s1 = [ "colors", "red", "blue", "green" ]
   s2 = [ "letters", "a", "b", "c" ]
   s3 = "foo"
   a  = [ s1, s2, s3 ]
   a.assoc("letters")  #=> [ "letters", "a", "b", "c" ]
   a.assoc("foo")      #=> nil

Returns the element at index. A negative index counts from the end of self. Returns nil if the index is out of range. See also Array#[].

   a = [ "a", "b", "c", "d", "e" ]
   a.at(0)     #=> "a"
   a.at(-1)    #=> "e"

Removes all elements from self.

   a = [ "a", "b", "c", "d", "e" ]
   a.clear    #=> [ ]

Invokes block once for each element of self. Creates a new array containing the values returned by the block. See also Enumerable#collect.

   a = [ "a", "b", "c", "d" ]
   a.collect {|x| x + "!" }   #=> ["a!", "b!", "c!", "d!"]
   a                          #=> ["a", "b", "c", "d"]

Invokes the block once for each element of self, replacing the element with the value returned by block. See also Enumerable#collect.

   a = [ "a", "b", "c", "d" ]
   a.collect! {|x| x + "!" }
   a             #=>  [ "a!", "b!", "c!", "d!" ]

When invoked with a block, yields all combinations of length n of elements from ary and then returns ary itself. The implementation makes no guarantees about the order in which the combinations are yielded.

When invoked without a block, returns an enumerator object instead.

Examples:

    a = [1, 2, 3, 4]
    a.combination(1).to_a  #=> [[1],[2],[3],[4]]
    a.combination(2).to_a  #=> [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
    a.combination(3).to_a  #=> [[1,2,3],[1,2,4],[1,3,4],[2,3,4]]
    a.combination(4).to_a  #=> [[1,2,3,4]]
    a.combination(0).to_a  #=> [[]] # one combination of length 0
    a.combination(5).to_a  #=> []   # no combinations of length 5

Returns a copy of self with all nil elements removed.

   [ "a", nil, "b", nil, "c", nil ].compact
                     #=> [ "a", "b", "c" ]

Removes nil elements from array. Returns nil if no changes were made.

   [ "a", nil, "b", nil, "c" ].compact! #=> [ "a", "b", "c" ]
   [ "a", "b", "c" ].compact!           #=> nil

Appends the elements in other_array to self.

   [ "a", "b" ].concat( ["c", "d"] ) #=> [ "a", "b", "c", "d" ]

Returns the number of elements. If an argument is given, counts the number of elements which equals to obj. If a block is given, counts the number of elements yielding a true value.

   ary = [1, 2, 4, 2]
   ary.count             # => 4
   ary.count(2)          # => 2
   ary.count{|x|x%2==0}  # => 3

Calls block for each element repeatedly n times or forever if none or nil is given. If a non-positive number is given or the array is empty, does nothing. Returns nil if the loop has finished without getting interrupted.

   a = ["a", "b", "c"]
   a.cycle {|x| puts x }  # print, a, b, c, a, b, c,.. forever.
   a.cycle(2) {|x| puts x }  # print, a, b, c, a, b, c.

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"

Deletes the element at the specified index, returning that element, or nil if the index is out of range. See also Array#slice!.

   a = %w( ant bat cat dog )
   a.delete_at(2)    #=> "cat"
   a                 #=> ["ant", "bat", "dog"]
   a.delete_at(99)   #=> nil

Deletes every element of self for which block evaluates to true.

   a = [ "a", "b", "c" ]
   a.delete_if {|x| x >= "b" }   #=> ["a"]

Drops first n elements from ary, and returns rest elements in an array.

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

Drops elements up to, but not including, the first element for which the block returns nil or false and returns an array containing the remaining elements.

   a = [1, 2, 3, 4, 5, 0]
   a.drop_while {|i| i < 3 }   # => [3, 4, 5, 0]

Calls block once for each element in self, passing that element as a parameter.

   a = [ "a", "b", "c" ]
   a.each {|x| print x, " -- " }

produces:

   a -- b -- c --

Same as Array#each, but passes the index of the element instead of the element itself.

   a = [ "a", "b", "c" ]
   a.each_index {|x| print x, " -- " }

produces:

   0 -- 1 -- 2 --

Returns true if self array contains no elements.

   [].empty?   #=> true

Returns true if array and other are the same object, or are both arrays with the same content.

Tries to return the element at position index. If the index lies outside the array, the first form throws an IndexError exception, the second form returns default, and the third form returns the value of invoking the block, passing in the index. Negative values of index count from the end of the array.

   a = [ 11, 22, 33, 44 ]
   a.fetch(1)               #=> 22
   a.fetch(-1)              #=> 44
   a.fetch(4, 'cat')        #=> "cat"
   a.fetch(4) { |i| i*i }   #=> 16

The first three forms set the selected elements of self (which may be the entire array) to obj. A start of nil is equivalent to zero. A length of nil is equivalent to self.length. The last three forms fill the array with the value of the block. The block is passed the absolute index of each element to be filled. Negative values of start count from the end of the array.

   a = [ "a", "b", "c", "d" ]
   a.fill("x")              #=> ["x", "x", "x", "x"]
   a.fill("z", 2, 2)        #=> ["x", "x", "z", "z"]
   a.fill("y", 0..1)        #=> ["y", "y", "z", "z"]
   a.fill {|i| i*i}         #=> [0, 1, 4, 9]
   a.fill(-2) {|i| i*i*i}   #=> [0, 1, 8, 27]

Returns the index of the first object in self such that is == to obj. If a block is given instead of an argument, returns first object for which block is true. Returns nil if no match is found.

   a = [ "a", "b", "c" ]
   a.index("b")        #=> 1
   a.index("z")        #=> nil
   a.index{|x|x=="b"}  #=> 1

This is an alias of find_index.

Returns the first element, or the first n elements, of the array. If the array is empty, the first form returns nil, and the second form returns an empty array.

   a = [ "q", "r", "s", "t" ]
   a.first     #=> "q"
   a.first(2)  #=> ["q", "r"]

Returns a new array that is a one-dimensional flattening of this array (recursively). That is, for every element that is an array, extract its elements into the new array. If the optional level argument determines the level of recursion to flatten.

   s = [ 1, 2, 3 ]           #=> [1, 2, 3]
   t = [ 4, 5, 6, [7, 8] ]   #=> [4, 5, 6, [7, 8]]
   a = [ s, t, 9, 10 ]       #=> [[1, 2, 3], [4, 5, 6, [7, 8]], 9, 10]
   a.flatten                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
   a = [ 1, 2, [3, [4, 5] ] ]
   a.flatten(1)              #=> [1, 2, 3, [4, 5]]

Flattens self in place. Returns nil if no modifications were made (i.e., array contains no subarrays.) If the optional level argument determines the level of recursion to flatten.

   a = [ 1, 2, [3, [4, 5] ] ]
   a.flatten!   #=> [1, 2, 3, 4, 5]
   a.flatten!   #=> nil
   a            #=> [1, 2, 3, 4, 5]
   a = [ 1, 2, [3, [4, 5] ] ]
   a.flatten!(1) #=> [1, 2, 3, [4, 5]]

Return true if this array is frozen (or temporarily frozen while being sorted).

Compute a hash-code for this array. Two arrays with the same content will have the same hash code (and will compare using eql?).

Returns true if the given object is present in self (that is, if any object == anObject), false otherwise.

   a = [ "a", "b", "c" ]
   a.include?("b")   #=> true
   a.include?("z")   #=> false

Returns the index of the first object in self such that is == to obj. If a block is given instead of an argument, returns first object for which block is true. Returns nil if no match is found.

   a = [ "a", "b", "c" ]
   a.index("b")        #=> 1
   a.index("z")        #=> nil
   a.index{|x|x=="b"}  #=> 1

This is an alias of find_index.

Replaces the contents of self with the contents of other_array, truncating or expanding if necessary.

   a = [ "a", "b", "c", "d", "e" ]
   a.replace([ "x", "y", "z" ])   #=> ["x", "y", "z"]
   a                              #=> ["x", "y", "z"]

Inserts the given values before the element with the given index (which may be negative).

   a = %w{ a b c d }
   a.insert(2, 99)         #=> ["a", "b", 99, "c", "d"]
   a.insert(-2, 1, 2, 3)   #=> ["a", "b", 99, "c", 1, 2, 3, "d"]

Create a printable version of array.

Returns a string created by converting each element of the array to a string, separated by sep.

   [ "a", "b", "c" ].join        #=> "abc"
   [ "a", "b", "c" ].join("-")   #=> "a-b-c"

Returns the last element(s) of self. If the array is empty, the first form returns nil.

   a = [ "w", "x", "y", "z" ]
   a.last     #=> "z"
   a.last(2)  #=> ["y", "z"]

Returns the number of elements in self. May be zero.

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

Invokes block once for each element of self. Creates a new array containing the values returned by the block. See also Enumerable#collect.

   a = [ "a", "b", "c", "d" ]
   a.collect {|x| x + "!" }   #=> ["a!", "b!", "c!", "d!"]
   a                          #=> ["a", "b", "c", "d"]

Invokes the block once for each element of self, replacing the element with the value returned by block. See also Enumerable#collect.

   a = [ "a", "b", "c", "d" ]
   a.collect! {|x| x + "!" }
   a             #=>  [ "a!", "b!", "c!", "d!" ]

When invoked with a block, yield all permutations of length n of the elements of ary, then return the array itself. If n is not specified, yield all permutations of all elements. The implementation makes no guarantees about the order in which the permutations are yielded.

When invoked without a block, return an enumerator object instead.

Examples:

    a = [1, 2, 3]
    a.permutation.to_a     #=> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
    a.permutation(1).to_a  #=> [[1],[2],[3]]
    a.permutation(2).to_a  #=> [[1,2],[1,3],[2,1],[2,3],[3,1],[3,2]]
    a.permutation(3).to_a  #=> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
    a.permutation(0).to_a  #=> [[]] # one permutation of length 0
    a.permutation(4).to_a  #=> []   # no permutations of length 4

Removes the last element from self and returns it, or nil if the array is empty.

If a number n is given, returns an array of the last n elements (or less) just like array.slice!(-n, n) does.

   a = [ "a", "b", "c", "d" ]
   a.pop     #=> "d"
   a.pop(2)  #=> ["b", "c"]
   a         #=> ["a"]

Returns an array of all combinations of elements from all arrays. The length of the returned array is the product of the length of ary and the argument arrays

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

Append—Pushes the given object(s) on to the end of this array. This expression returns the array itself, so several appends may be chained together.

   a = [ "a", "b", "c" ]
   a.push("d", "e", "f")
           #=> ["a", "b", "c", "d", "e", "f"]

Searches through the array whose elements are also arrays. Compares obj with the second element of each contained array using ==. Returns the first contained array that matches. See also Array#assoc.

   a = [ [ 1, "one"], [2, "two"], [3, "three"], ["ii", "two"] ]
   a.rassoc("two")    #=> [2, "two"]
   a.rassoc("four")   #=> nil

Returns a new array containing the items in self for which the block is not true.

Equivalent to Array#delete_if, deleting elements from self for which the block evaluates to true, but returns nil if no changes were made. Also see Enumerable#reject.

Replaces the contents of self with the contents of other_array, truncating or expanding if necessary.

   a = [ "a", "b", "c", "d", "e" ]
   a.replace([ "x", "y", "z" ])   #=> ["x", "y", "z"]
   a                              #=> ["x", "y", "z"]

Returns a new array containing self‘s elements in reverse order.

   [ "a", "b", "c" ].reverse   #=> ["c", "b", "a"]
   [ 1 ].reverse               #=> [1]

Reverses self in place.

   a = [ "a", "b", "c" ]
   a.reverse!       #=> ["c", "b", "a"]
   a                #=> ["c", "b", "a"]

Same as Array#each, but traverses self in reverse order.

   a = [ "a", "b", "c" ]
   a.reverse_each {|x| print x, " " }

produces:

   c b a

Returns the index of the last object in array == to obj. If a block is given instead of an argument, returns first object for which block is true. Returns nil if no match is found.

   a = [ "a", "b", "b", "b", "c" ]
   a.rindex("b")        #=> 3
   a.rindex("z")        #=> nil
   a.rindex{|x|x=="b"}  #=> 3

Choose a random element, or the random n elements, from the array. If the array is empty, the first form returns nil, and the second form returns an empty array.

Invokes the block passing in successive elements from array, returning an array containing those elements for which the block returns a true value (equivalent to Enumerable#select).

   a = %w{ a b c d e f }
   a.select {|v| v =~ /[aeiou]/}   #=> ["a", "e"]

Returns the first element of self and removes it (shifting all other elements down by one). Returns nil if the array is empty.

If a number n is given, returns an array of the first n elements (or less) just like array.slice!(0, n) does.

   args = [ "-m", "-q", "filename" ]
   args.shift     #=> "-m"
   args           #=> ["-q", "filename"]

   args = [ "-m", "-q", "filename" ]
   args.shift(2)  #=> ["-m", "-q"]
   args           #=> ["filename"]

Returns a new array with elements of this array shuffled.

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

Shuffles elements in self in place.

Alias for length

Element Reference—Returns the element at index, or returns a subarray starting at start and continuing for length elements, or returns a subarray specified by range. Negative indices count backward from the end of the array (-1 is the last element). Returns nil if the index (or starting index) are out of range.

   a = [ "a", "b", "c", "d", "e" ]
   a[2] +  a[0] + a[1]    #=> "cab"
   a[6]                   #=> nil
   a[1, 2]                #=> [ "b", "c" ]
   a[1..3]                #=> [ "b", "c", "d" ]
   a[4..7]                #=> [ "e" ]
   a[6..10]               #=> nil
   a[-3, 3]               #=> [ "c", "d", "e" ]
   # special cases
   a[5]                   #=> nil
   a[5, 1]                #=> []
   a[5..10]               #=> []

Deletes the element(s) given by an index (optionally with a length) or by a range. Returns the deleted object, subarray, or nil if the index is out of range.

   a = [ "a", "b", "c" ]
   a.slice!(1)     #=> "b"
   a               #=> ["a", "c"]
   a.slice!(-1)    #=> "c"
   a               #=> ["a"]
   a.slice!(100)   #=> nil
   a               #=> ["a"]

Returns a new array created by sorting self. Comparisons for the sort will be done using the <=> operator or using an optional code block. The block implements a comparison between a and b, returning -1, 0, or +1. See also Enumerable#sort_by.

   a = [ "d", "a", "e", "c", "b" ]
   a.sort                    #=> ["a", "b", "c", "d", "e"]
   a.sort {|x,y| y <=> x }   #=> ["e", "d", "c", "b", "a"]

Sorts self. Comparisons for the sort will be done using the <=> operator or using an optional code block. The block implements a comparison between a and b, returning -1, 0, or +1. See also Enumerable#sort_by.

   a = [ "d", "a", "e", "c", "b" ]
   a.sort                    #=> ["a", "b", "c", "d", "e"]
   a.sort {|x,y| y <=> x }   #=> ["e", "d", "c", "b", "a"]

Sorts array in place using a set of keys generated by mapping the values in array through the given block.

Returns first n elements from ary.

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

Passes elements to the block until the block returns nil or false, then stops iterating and returns an array of all prior elements.

   a = [1, 2, 3, 4, 5, 0]
   a.take_while {|i| i < 3 }   # => [1, 2]

Returns self. If called on a subclass of Array, converts the receiver to an Array object.

Returns self.

Alias for inspect

Assumes that self is an array of arrays and transposes the rows and columns.

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

Returns a new array by removing duplicate values in self.

   a = [ "a", "a", "b", "b", "c" ]
   a.uniq   #=> ["a", "b", "c"]
   c = [ "a:def", "a:xyz", "b:abc", "b:xyz", "c:jkl" ]
   c.uniq {|s| s[/^\w+/]}  #=> [ "a:def", "b:abc", "c:jkl" ]

Removes duplicate elements from self. Returns nil if no changes are made (that is, no duplicates are found).

   a = [ "a", "a", "b", "b", "c" ]
   a.uniq!   #=> ["a", "b", "c"]
   b = [ "a", "b", "c" ]
   b.uniq!   #=> nil
   c = [ "a:def", "a:xyz", "b:abc", "b:xyz", "c:jkl" ]
   c.uniq! {|s| s[/^\w+/]}  #=> [ "a:def", "b:abc", "c:jkl" ]

Prepends objects to the front of array. other elements up one.

   a = [ "b", "c", "d" ]
   a.unshift("a")   #=> ["a", "b", "c", "d"]
   a.unshift(1, 2)  #=> [ 1, 2, "a", "b", "c", "d"]

Returns an array containing the elements in self corresponding to the given selector(s). The selectors may be either integer indices or ranges. See also Array#select.

   a = %w{ a b c d e f }
   a.values_at(1, 3, 5)
   a.values_at(1, 3, 5, 7)
   a.values_at(-1, -3, -5, -7)
   a.values_at(1..3, 2...5)

Converts any arguments to arrays, then merges elements of self with corresponding elements from each argument. This generates a sequence of self.size n-element arrays, where n is one more that the count of arguments. If the size of any argument is less than enumObj.size, nil values are supplied. If a block given, it is invoked for each output array, otherwise an array of arrays is returned.

   a = [ 4, 5, 6 ]
   b = [ 7, 8, 9 ]
   [1,2,3].zip(a, b)      #=> [[1, 4, 7], [2, 5, 8], [3, 6, 9]]
   [1,2].zip(a,b)         #=> [[1, 4, 7], [2, 5, 8]]
   a.zip([1,2],[8])       #=> [[4,1,8], [5,2,nil], [6,nil,nil]]

Set Union—Returns a new array by joining this array with other_array, removing duplicates.

   [ "a", "b", "c" ] | [ "c", "d", "a" ]
          #=> [ "a", "b", "c", "d" ]