Programming

Some coding examples.

Quicksort algorithm

This example implements the quicksort algorithm using native Hansl code. It is compared to the built-in function msortby() which is written in C -- and hence much quicker ;-)

set verbose off
clear

function matrix quicksort (matrix m)
/* Implementation of the divide-and-conquer quicksort algorithm.
   For details see here: https://en.wikipedia.org/wiki/Quicksort */

    m = vec(m)

    scalar nrows = rows(m)
    if nrows < 2
        return m
    endif

    matrix smaller, bigger
    scalar pivot = m[1]
    scalar steps = 1 + rows(m[2:])

    loop i=2..steps
        if m[i] <= pivot
            smaller |= m[i]
        else
            bigger |= m[i]
        endif
    endloop

    return quicksort(smaller) | pivot | quicksort(bigger)
end function

# Some random vector
matrix m = mrandgen(t, 14, 1e5, 1)

set stopwatch
matrix r = quicksort(m)
printf "quicksort() took %g seconds\n", $stopwatch

set stopwatch
matrix z = msortby(m, 1)
printf "msortby() took %g seconds\n", $stopwatch

# Check for equality
assert(sum(r - z) == 0)