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Diffstat (limited to 'doc/lispref/sequences.texi')
-rw-r--r-- | doc/lispref/sequences.texi | 40 |
1 files changed, 4 insertions, 36 deletions
diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi index 6322f17e77b..de83b96d748 100644 --- a/doc/lispref/sequences.texi +++ b/doc/lispref/sequences.texi @@ -440,6 +440,10 @@ where @var{predicate} is the @code{:lessp} argument. When using this form, sorting is always done in-place. @end defun +@xref{Sorting}, for more functions that perform sorting. See +@code{documentation} in @ref{Accessing Documentation}, for a useful +example of @code{sort}. + @cindex comparing values @cindex standard sorting order @anchor{definition of value<} @@ -476,42 +480,6 @@ Examples: @end example @end defun -Sometimes, computation of sort keys of list or vector elements is -expensive, and therefore it is important to perform it the minimum -number of times. By contrast, computing the sort keys of elements -inside the @var{predicate} function passed to @code{sort} will generally -perform this computation each time @var{predicate} is called with some -element. If you can separate the computation of the sort key of an -element into a function of its own, you can use the following sorting -function, which guarantees that the key will be computed for each list -or vector element exactly once. - -@cindex decorate-sort-undecorate -@cindex Schwartzian transform -@defun sort-on sequence predicate accessor -This function stably sorts @var{sequence}, which can be a list, a -vector, a bool-vector, or a string. It sorts by comparing the sort -keys of the elements using @var{predicate}. The comparison function -@var{predicate} accepts two arguments, the sort keys to compare, and -should return non-@code{nil} if the element corresponding to the first -key should sort before the element corresponding to the second key. The -function computes a sort key of each element by calling the -@var{accessor} function on that element; it does so exactly once for -each element of @var{sequence}. The @var{accessor} function is called -with a single argument, an element of @var{sequence}. - -This function implements what is known as @dfn{decorate-sort-undecorate} -paradigm, or the Schwartzian transform. It basically trades CPU for -memory, creating a temporary list with the computed sort keys, then -mapping @code{car} over the result of sorting that temporary list. -Unlike with @code{sort}, the return value is always a new list; the -original @var{sequence} is left intact. -@end defun - -@xref{Sorting}, for more functions that perform sorting. See -@code{documentation} in @ref{Accessing Documentation}, for a useful -example of @code{sort}. - @cindex sequence functions in seq @cindex seq library @cindex sequences, generalized |