December 2017 Archives

I Still Haven't Found What I'm Looking For

Last time we took a look at a selection of sorting operations that we can use to sort arrays, or ranges of elements within them. After defining some useful comparison functions satisfying JavaScript's requirement of returning a negative number when the first argument compares smaller than the second, zero when they compare equal and a positive number otherwise, and a function to map negative integers to indices read from the end of arrays in the same way that Array.slice does, we first implemented ak.partition which divides elements into two ranges; those elements that satisfy some given condition followed by those elements that don't. We saw how this could be used to implement the quicksort algorithm but instead defined ak.sort to sort a range of elements using Array.sort, slicing them out beforehand and splicing them back in again afterwards if they didn't represent whole arrays. We did use it, however, to implement ak.nthElement which puts a the correctly sorted element in a given position position within a range, putting before it elements that are no greater and after it elements that are no smaller. Finally, we implemented ak.partialSort which puts every element in a range up to, but not including, a given position into its correctly sorted place with all of the elements from that position onwards comparing no less than the last correctly sorted element.
This time we shall take a look at some of the ways that we can query data after we have manipulated it with these functions.

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