Instance Methods

Question 1

join

Answer 1

Fn: Return a string which is the values in the array converted to strings and concatenated.
Returns: string
Syntax: my_array.join(separator)

Question 2

#shuffle
#shuffle!

Answer 2

Fn: put the array items in random order
Returns: Array (!) or new array

Question 3

each

Answer 3

Function: Iterates through the array, applying the block once to each item
Returns: The original array
Syntax: my_array.each {|item| block}
(Returns Enumerator if no block is given)

Question 4

#map
#map!
#collect
#collect!

Answer 4

Fn: Transform an array by iterating through and passing each element as a parameter.
Returns: The first method returns a new array.
The second, with the bang suffix, mutates the original array in place and returns it.
Syntax: same as #each
(Returns Enumerator if no block is given)

Question 5

#uniq
#uniq!

Answer 5

Fn: removes duplicates. Use return value of block for comparison
Returns: array (!) or new array
Syntax: my_array.uniq{|item|}

Question 6

#sort_by
#sort_by!

Answer 6

Fn: sort using a set of keys generated by mapping the values in the array through the given block
Returns: a new array (or mutates array in place when !)
Syntax: my_array.sort_by{|object| block}

Question 7

keep_if

Answer 7

Fn: evaluates the block and deletes every element from the array for which it evaluates to false
Returns: the original array
Syntax: same as #delete_if

Question 8

each_index

Answer 8

Function: Like each, but passes the index of the element instead of the element itself
Returns: the original array
Syntax: my_array.each_index{|item| block}

Question 9

#take
#drop

Answer 9

Fn: take is like first(n). Drop returns the elements after the first n (i.e. the remaining ones)
Returns: new array
Syntax: my_array.take(n)

Question 10

delete

Answer 10

Fn: destructively remove an element from the array matching obj
Returns: the last deleted item
Syntax: my_array.delete(obj)

Question 11

values_at

Answer 11

Fn: return the values at the given indices
Returns: new array
Syntax: my_array.values_at(int1, in2… or a range)

Question 12

+ / #concat

Answer 12

Fn: concatenate two arrays
Returns: a new array
Syntax: my_array + other_array

Question 13

#rotate
#rotate!

Answer 13

Fn: rotates the array elements so that count is the first element
Returns: Array (!) or new array
Syntax: my_array.rotate(count=n)

Question 14

delete_at

Answer 14

Fn: destructively remove the object found at a given index
Returns: the deleted object or nil if not found
Syntax: my_array.delete_at(idx)

Question 15

#flatten
#flatten!

Answer 15

Fn: make a one dimensional array
Returns: array (!) or a new array
Syntax: my_array.flatten([level])

Question 16

#difference
[ ]-

Answer 16

Makes a new array that is a copy of the receiver, minus the duplicates, preserving order

Question 17

#first
#last

Answer 17

Fn: return the first/last (or first/last n) elements from the array
Returns: either the element or an array of n elements
Syntax: my_array.first(n)

Question 18

#slice
#slice!

Answer 18

Fn: return a sub-array starting at idx, for a given length/range (optional)
Returns: the array (!) or a new array
Syntax: my_array.slice(idx,length/range) or nil

Question 19

insert

Answer 19

Fn: Inserts object after idx
Returns: the array
Syntax: my_array.insert(idx, obj)

Question 20

to_s / #inspect

Answer 20

Fn: returns the string interpretation of the array
Returns: a string

Question 21

length / #size

Answer 21

Returns number of elements in array

Question 22

#empty?
#include?(obj)

Answer 22

These return Boolean values after checking if the array is empty or if it contains (obj)

Question 23

#union
|

Answer 23

Joins arrays, excluding duplicates, preserving order

Question 24

transpose

Answer 24

Given an array of arrays transposes the rows and columns

Question 25

#shift
#pop

Answer 25

Fn: remove the first/last element from the array
Returns: the removed element (or nil)
Syntax: my_array.shift

Question 26

#select
#select!
#filter
#filter!

Answer 26

Fn: iterates through the array, passing each element as parameter to the block and returning it if the block evaluates to ‘true’
Returns: a new array containing the selected results (the methods with a bang suffix mutate the array in place)
Syntax: same as #each
(Returns Enumerator if no block is given)

Question 27

#reverse
#reverse!

Answer 27

Fn: put the array elements in reverse order
Returns: the array(!) or a new array

Question 28

sample

Answer 28

Fn: Choose a random element from the array

See docs for further usage

Question 29

fetch(idx)

Answer 29

Fn: This is the most basic usage which returns the element at idx

Question 30

#sort
#sort!

Answer 30

Fn: comparisons for the sort are done using the <=> operator or an optional code block… the block implements a comparison of a & b
Returns: a new array
Syntax: my_array.sort{|a, b| block}

Question 31

#unshift
#push / #<

Answer 31

Fn: prepend/append the given object onto the array
Returns: the array
Syntax: my_array.unshift(obj)

Question 32

take_while

Answer 32

Fn: Passes elements to the block until it returns false/nil
Returns: a new array
Syntax: my_array.take_while{|obj| block }

Question 33

delete_if

Answer 33

Fn: Delete from the array if the block evaluates to true
Returns: original array
Syntax: my_array.delete_if{|item| block}