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Merge pull request #3987 from quickfur/schwartzSort-doc

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Improve schwartzSort documentation.
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Robert Schadek 2016-02-12 18:53:03 +01:00
commit c548dbfbb4
1 changed files with 17 additions and 8 deletions
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25
std/algorithm/sorting.d
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@ -998,6 +998,9 @@ always satisfy these conditions for floating point types, because the expression
will always be $(D false) when either $(D a) or $(D b) is NaN.
Use $(XREF math, cmp) instead.
If `less` involves expensive computations on the _sort key, it may be
worthwhile to use $(LREF schwartzSort) instead.
Params:
less = The predicate to sort by.
ss = The swapping strategy to use.
@ -2003,14 +2006,20 @@ unittest
// schwartzSort
/**
Sorts a range using an algorithm akin to the $(WEB
wikipedia.org/wiki/Schwartzian_transform, Schwartzian transform), also
known as the decorate-sort-undecorate pattern in Python and Lisp.
This function is helpful when the sort comparison includes
an expensive computation. The complexity is the same as that of the
corresponding $(D sort), but $(D schwartzSort) evaluates $(D
transform) only $(D r.length) times (less than half when compared to
regular sorting). The usage can be best illustrated with an example.
Alternative sorting method that should be used when comparing keys involves an
expensive computation. Instead of using `less(a, b)` for comparing elements,
`schwartzSort` uses `less(transform(a), transform(b))`. The values of the
`transform` function are precomputed in a temporary array, thus saving on
repeatedly computing it. Conversely, if the cost of `transform` is small
compared to the cost of allocating and filling the precomputed array, `sort`
may be faster and therefore preferable.
This approach to sorting is akin to the $(WEB
wikipedia.org/wiki/Schwartzian_transform, Schwartzian transform), also known as
the decorate-sort-undecorate pattern in Python and Lisp. The complexity is the
same as that of the corresponding `sort`, but `schwartzSort` evaluates
`transform` only `r.length` times (less than half when compared to regular
sorting). The usage can be best illustrated with an example.
Example:
----