array

enclosed with [ ]

 

can contain elements with different classes

  

add element to array:

use <<

ex:

a=[]

a <<>

array adding
ex:
[“test1”] + [“test2”]
-->  [ “test1”,  “test2” ]

use concat:

ex:

[1,2].concat([3,4])

--> [1,2,3,4]

concat modifies original array

<<:

add element to array

ex:

a=[1,2]

a<<3

---> [1,2,3]

new:

ex:

Array.new(3, "a")

create a three element array ,with each initialized to "a"

a=0

Array.new(3) { a=a+1 }

create a three element array , [1,2,3]

get more than one elements

ex:

a=[1,2,3,4,5]

a[3,2] 

--->  [4,5]

sort_by

accept block argument

ex:

sort_by{ rand }

sort randomly 

join:

[“a”, “b”, “c”].join(‘2’)

-->  “a2b2c”

push:

add an element to the end of the array

pop:

remove last element

include:

ex:

[1, 2, 3].include?(1)

--->  true

uniq:

ex:

["ab", "c","ab"].uniq

--->["ab", "c"]

multiplication:

ex:

[1,2]*2

--> [1,2, 1,2]

detect:

find the first element that match condition in the array

ex:

[1 , 2, 3].detect { | i |  i>2 }

--> 3

find:

find first element that matches  

find_all:

find all elements that match condition in the array

ex:

[1,2,3].find_all{ |i| i>1 }

-->  [2, 3]

array intersection:

use &

ex:

[1,2,3] & [2,3]

--> [2,3]

%w[a b]

--> ["a",  "b"]

sort:

ex:

c=[ [1, 2], [3, 1] ]

c.sort{ |a, b| a[0]<=>b[0] }

-->  [ [1,2], [3, 1] ]

c.sort{ |a, b| b[0]<=>a[0] } 

-->   [[3, 1], [1, 2]]

c.sort{ |a, b| a[1]<=>b[1] } 

-->   [[3, 1], [1, 2]]

a[0] <=> b[0] compare first element of nested array in ascending order

a[1] <=> b[1] compare second element of nested array in ascending order

b[0] <=> b[1] compare first element of nested array in descending order

unshift:

add an element to the beginning of the array

shift:

remove the first element 

zip:

ex:

[1,2].zip([3,4])

--> [ [1,3],  [2,4] ]

flatten:

ex:

[1,2, [3,4] ].flatten

--> [1,2,3,4]

reject:

ex:

[1,2,3].reject { |item|  item>2 }

---> [1,2]

replace, reverse:

each, each_with_index

include?,  empty?, any?, all?

ex:

[1,2,3].any?{ | k|  k>2 }

---> true

index:

return the first element equals to parameter

ex:

["a", "b", "c"].index( "b")

---> 1

index   with  integer <0

count from right

ex:

a= [1, 2, 3]

a[-1]  

--->  3

compact:

remove nil element from the array