ruby 学习 -- Array --2

[1, 2, 3] # An array that holds three Fixnum objects
[-10...0, 0..10,] # An array of two ranges; trailing commas are allowed
[[1,2],[3,4],[5]] # An array of nested arrays
[x+y, x-y, x*y] # Array elements can be arbitrary expressions
[] # The empty array has size 0

# %w and %W introduce an array literal, much like %q and %Q introduce a String literal
words = %w[this is a test] # Same as: [‘this‘, ‘is‘, ‘a‘, ‘test‘]
open = %w| ( [ { < | # Same as: [‘(‘, ‘[‘, ‘{‘, ‘<‘]
white = %W(\s \t \r \n) # Same as: ["\s", "\t", "\r", "\n"]

empty = Array.new # []: returns a new empty array
nils = Array.new(3) # [nil, nil, nil]: new array with 3 nil elements
zeros = Array.new(4, 0) # [0, 0, 0, 0]: new array with 4 0 elements
copy = Array.new(nils) # Make a new copy of an existing array
count = Array.new(3) {|i| i+1} # [1,2,3]: 3 elements computed from index

a = [0, 1, 4, 9, 16] # Array holds the squares of the indexes
a[0] # First element is 0
a[-1] # Last element is 16
a[-2] # Second to last element is 9
a[a.size-1] # Another way to query the last element
a[-a.size] # Another way to query the first element
a[8] # Querying beyond the end returns nil
a[-8] # Querying before the start returns nil, too

a = (‘a‘..‘e‘).to_a # Range converted to [‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘]
a[0,0] # []: this subarray has zero elements
a[1,1] # [‘b‘]: a one-element array
a[-2,2] # [‘d‘,‘e‘]: the last two elements of the array
a[0..2] # [‘a‘, ‘b‘, ‘c‘]: the first three elements
a[-2..-1] # [‘d‘,‘e‘]: the last two elements of the array
a[0...-1] # [‘a‘, ‘b‘, ‘c‘, ‘d‘]: all but the last element

a[0] = "zero" # a is ["zero", 1, 4, 9, 16]
a[-1] = 1..16 # a is ["zero", 1, 4, 9, 1..16]
a[8] = 64 # a is ["zero", 1, 4, 9, 1..16, nil, nil, nil, 64]
a[-9] = 81 # Error: can‘t assign before the start of an array

a[0,2] = [‘A‘, ‘B‘] # a becomes [‘A‘, ‘B‘, ‘c‘, ‘d‘, ‘e‘]
a[2...5]=[‘C‘, ‘D‘, ‘E‘] # a becomes [‘A‘, ‘B‘, ‘C‘, ‘D‘, ‘E‘]
a[0,0] = [1,2,3] # Insert elements at the beginning of a
a[0..2] = [] # Delete those elements
a[-1,1] = [‘Z‘] # Replace last element with another
a[-1,1] = ‘Z‘ # For single elements, the array is optional
a[-2,2] = nil # Delete last 2 elements in 1.8; replace with nil in 1.9

a = [1, 2, 3] + [4, 5] # [1, 2, 3, 4, 5]
a = a + [[6, 7, 8]] # [1, 2, 3, 4, 5, [6, 7, 8]]
a = a + 9 # Error: righthand side must be an array

[‘a‘, ‘b‘, ‘c‘, ‘b‘, ‘a‘] - [‘b‘, ‘c‘, ‘d‘] # [‘a‘, ‘a‘]

a = [] # Start with an empty array
a << 1 # a is [1]
a << 2 << 3 # a is [1, 2, 3]
a << [4,5,6] # a is [1, 2, 3, [4, 5, 6]]

a = [0] * 8 # [0, 0, 0, 0, 0, 0, 0, 0]

a = [1, 1, 2, 2, 3, 3, 4]
b = [5, 5, 4, 4, 3, 3, 2]
a | b # [1, 2, 3, 4, 5]: duplicates are removed
b | a # [5, 4, 3, 2, 1]: elements are the same, but order is different
a & b # [2, 3, 4]
b & a # [4, 3, 2]