Ruby: Array

What is Array

Array is a ordered sequence of items. In ruby, each element can be of any Value Type, and you can add items or delete items in array. (it can grow or shrink)

Create Array

Create array using array literal expression.

xx = [0, 1, 2, "a"]
p xx == [0, 1, 2, "a"]

Create array using Array function.

# create a array of 3 elements, each is nil
bb = Array.new(3)
p bb == [nil, nil, nil]

# create array of 3 elements, each is 1
cc = Array.new(3,1)
p cc == [1, 1, 1]

Length (Count of Elements)

xx = ["b", 4, 6]
p xx.length == 3

Get a Element

Array element can be extracted by appending a square bracket with index.

array[index]

xx = ["a","b","c"]
p xx[0] == "a"
p xx[1] == "b"

Negative index counts from right.

xx = ["a","b","c"]
p xx[-1] == "c"

Get Sub-Array (Slice)

Consecutive elements can be extracted using the form

array[startIndex, count]

xx = [ "a", "b", "c", "d"]
p xx[1,2] == ["b", "c"]
# first is index, second is count

Change Element

A element can be changed with the form

array[index] = new_value

xx = [0, 1, 2]
xx[2] = "b"
p xx == [0, 1, "b"]

A slice (continuous sequence) of elements can be changed by assigning to a array directly. The length of the slice need not match the length of new array.

xx = [0,1,2,3,4]

# change 4 elements of array to a new array, starting at index 2
xx[2,4] = ["x", "y"]
p xx == [0, 1, "x", "y"]

Nested Array

Array can be nested arbitrarily. Append extra bracket to get element of nested array.

xx = [3, 4, [7, 8]]
p xx[2][1] == 8

Add element

xx = [0, 1, 2]

p xx.insert(1,"b") == [0, "b", 1, 2]

p xx == [0, "b", 1, 2]

Appending element

# appending to array

xx = [0, 1]
xx << 2
p xx == [0, 1, 2]

xx << [5, 6]
p xx == [0, 1, 2, [5, 6]]

Delete Element

aa = [0, "b", 2]

aa.delete_at(1) == "b"
p aa == [0, 2]

Push and Pop

Append/Remove from the end, and modify variable.

xx = [0, 1, 2]

# add a element to the end
p xx.push("a") == [0, 1, 2, "a"]

# original array also changed
p xx == [0, 1, 2, "a"]

# pop removes the last element, and returns that
p xx.pop == "a"

p xx == [0, 1, 2]

Join Arrays

Array can be joined with plus sign.

xx = ["a", "b"] + [7, 6]
p xx == ["a", "b", 7, 6]

Find the index of a element

xx = ["a","b","c"]
p xx.index("b") == 1

# not found, return nil
p xx.index("d") == nil

Array Union, Intersection, Difference

aa = [0, 8, 7, 3, 1]
bb = [3, 4]

# difference
p aa - bb == [0, 8, 7, 1]

# intersection
p aa & bb == [3]

# union
p aa | bb == [0, 8, 7, 3, 1, 4]

Get uniq elements

xx = [0, 7, 3, 7]

# uniq
p xx.uniq == [0, 7, 3]

# original array not modified
p xx == [0, 7, 3, 7]

# uniq, modify original array
xx.uniq!
p xx == [0, 7, 3]

Sorting array

xx = [0, 4, 2]

xx.sort == [0, 2, 4]

# original not changed
p xx == [0, 4, 2]

# change original
xx.sort! == [0, 2, 4]
p xx == [0, 2, 4]

Array equality test

aa = [0, 1, 2]
bb = [0, 1, 2.0]
cc = [0, 1, "2"]

# check if 2 arrays are the same (ignores type.)
p ((aa == bb) == true)
p ((aa == cc) == false)

# check if 2 arrays are the same, and each element has the same type
p (aa.eql?(bb) == false)