
Sorting Algorithm

This is a sorting algorithm.   It may be applied to a set of data in order to sort it.    
For comparing various sorts, see compare sorts.  
For other sorting algorithms,   see sorting algorithms,   or:

O(n logn) sorts
Heap sort |
Merge sort |
Patience sort |
Quick sort
O(n log2n) sorts
Shell Sort
O(n2) sorts
Bubble sort |
Cocktail sort |
Cocktail sort with shifting bounds |
Comb sort |
Cycle sort |
Gnome sort |
Insertion sort |
Selection sort |
Strand sort
other sorts
Bead sort |
Bogo sort |
Common sorted list |
Composite structures sort |
Custom comparator sort |
Counting sort |
Disjoint sublist sort |
External sort |
Jort sort |
Lexicographical sort |
Natural sorting |
Order by pair comparisons |
Order disjoint list items |
Order two numerical lists |
Object identifier (OID) sort |
Pancake sort |
Quickselect |
Permutation sort |
Radix sort |
Ranking methods |
Remove duplicate elements |
Sleep sort |
Stooge sort |
[Sort letters of a string] |
Three variable sort |
Topological sort |
Tree sort


Use the quickselect algorithm on the vector

 [9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
To show the first, second, third, ... up to the tenth largest member of the vector, in order, here on this page.

 Note: Quicksort has a separate task. 


function partition (list, left, right, pivotIndex)
    local pivotValue = list[pivotIndex]
    list[pivotIndex], list[right] = list[right], list[pivotIndex]
    local storeIndex = left
    for i = left, right do
        if list[i] < pivotValue then
            list[storeIndex], list[i] = list[i], list[storeIndex]
            storeIndex = storeIndex + 1
        end
    end
    list[right], list[storeIndex] = list[storeIndex], list[right]
    return storeIndex
end
 
function quickSelect (list, left, right, n)
    local pivotIndex
    while 1 do
        if left == right then return list[left] end
        pivotIndex = math.random(left, right)
        pivotIndex = partition(list, left, right, pivotIndex)
        if n == pivotIndex then
            return list[n]
        elseif n < pivotIndex then
            right = pivotIndex - 1
        else
            left = pivotIndex + 1
        end
    end
end
 
math.randomseed(os.time())
local vec = {9, 8, 7, 6, 5, 0, 1, 2, 3, 4}
for i = 1, 10 do print(i, quickSelect(vec, 1, #vec, i) .. " ") end