Note: Ruby Core Methods of Array (2.6.3)
Arrays are ordered, integer-indexed collection of any object.
Assume ary = Array.new([1,2,3,4]) = [1,2,3,4]
Operator
& = and
| = or
<=> compare
Getting Element by Index:
Array.at(index) — input index number give particular data
ary.at(0)=ary[0]=1
# Array.fetch — Works same as “at”, but return “Error” if index out of bound while at will return nil
Array.index(element) — give element return its index
Array.first , Array.last — return first(0) and last (-1) element
Array.take(n) e— Get First n element
Array.drop(n) — Get all other element after n
Array.dig(n1,n2…) — Return value from nested array while n represent index in each level.
# [[1,[2,3]]].dig(0,1,1) = 3
Get Information of array
Array.length = Array.size = Array.count : Get numbers of element in array
# Count can add counting cirtera with block
Array.empty? — Check whether array is empty
Array.include?(element) — Check whether array include given element
Adding
Array.push(element) = Array <<element — Add new element as latest
# Array.append do the same
Array.concat(other array) — Add new array at last
Array + other array — Create new array and add other array at last
Array.unshift(element) — -Add new element at first and shift other back
Array.insert(index,*element) — Add one or more element at index
Remove
# Most methods here will effect origin array
#Except compact and uniq unless you use “!” version
Array.pop — delete the last element
Array.shift — return first element and remove from array
Array.delete_at(index) — delete specific element
Array.delete(element) — delete all that element(can be more than one)
Array.compact — remove all nil
Array.uniq — return unique element
Change
Array.reverse — Reverse the array
Array.sort {a, b a<=>b} — Sort the element with given criteria and Create new array.
# a<=>b is ascending(default), b<=>a is descending
# Can be replaced by other criteria, such as comparing the length of element: a.length<=>b.length
Array.rotate(n) —Rotating and set n index as the beginning of new array
Array.fill
Array.replace(another array) — replace all the element with the argument
Iterating
Array.each {}— Iterating and yield each element to block
Array.each_index — Same as each but run with index
Array.reverse_index — Iterating from back to front
Array.map{}— similar to each, but will create a new array in the end
# Array.collect do the same thing
Selecting/Filtering
Array.select{} — Return an array with selected element (criteria is in block)
#Array.keep_if — Similar to select but effect origin array
Array.reject{} =Array.drop_while— Return an array with unselected element
#Array.delete_if — Similar to reject but effect origin array
Array.difference(other array(s)) — compare and return array include element only in origin array. Can also use “-” to represent this function.
EX:[1,1,2,3,3,4,5] — [1,5,6] = [2,3,3,4]
## It does not work in my pc at this point. Wait for more inspection.
Array.max/min {|a,b| a<=>b} — Similar to #sort, find the max/min element (n th if input) with give criteria
Array.assco(element) — Return a sub-array whose first element is matched
Array.rassco(element) — Second element version of Array#assco
Array.flatten — Create a one-dimension array of given nested array.
# Can input level argument to decide to flatten the array up to which level.
Statistic method
Array.sample — Randomly select 1 or n (if given) element from array
Array.shuffle — Randomly reorder the array
Array.product(other array(s)) — Return array of all combination of all elements of all arrays
Array.permutation(n) — Yield all permutation of n length element (nPm)
# In detail, it returns an Enumerator object, so should use to_a to switch it to an array.
Array.repeated_permutation(n) — Yield all permutation of n length element(nHm)
# Same as permutation, require to apply to_a to get array
Array.combination(n) — Yield all combination of n length element(nCm)
Other
Array.join(separator) —Return string of all elements combined with a separator
Array.transpose —Transpose the matrix’s row and column
