Decorate-sort-undecorate idiom: Difference between revisions
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{{task}}
[[Category:Sorting]]
;Introduction
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<pre>
a is Code site Rosetta programming chrestomathy
</pre>
=={{header|C++}}==
<syntaxhighlight lang="cpp">#include <algorithm>
#include <iostream>
#include <type_traits>
#include <vector>
template <typename Iterator, typename Function>
void decorate_sort_undecorate(Iterator begin, Iterator end, Function f) {
using ValueType = typename std::iterator_traits<Iterator>::value_type;
using KeyType = std::invoke_result_t<Function, ValueType>;
using KeyValue = std::pair<KeyType, ValueType>;
std::vector<KeyValue> tmp;
tmp.reserve(std::distance(begin, end));
std::transform(begin, end, std::back_inserter(tmp), [&f](ValueType& v) {
return std::make_pair(f(v), std::move(v));
});
std::sort(tmp.begin(), tmp.end(), [](const KeyValue& a, const KeyValue& b) {
return a.first < b.first;
});
std::transform(tmp.begin(), tmp.end(), begin,
[](KeyValue& p) { return std::move(p.second); });
}
int main() {
std::string test[] = {"Rosetta", "Code", "is", "a",
"programming", "chrestomathy", "site"};
decorate_sort_undecorate(std::begin(test), std::end(test),
[](const std::string& s) { return s.size(); });
for (const std::string& s : test)
std::cout << s << ' ';
std::cout << '\n';
}</syntaxhighlight>
{{out}}
<pre>
a is Code site Rosetta programming chrestomathy
</pre>
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'''Solution'''
Let us create an array for testing:
[[File:Fōrmulæ - Decorate-sort-undecorate idiom 01.png]]
'''Decorate-sort-undecorate:''' The following is a solution using a decorate-sort-undecorate idiom:
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[[File:Fōrmulæ - Decorate-sort-undecorate idiom 03.png]]
[[File:Fōrmulæ - Decorate-sort-undecorate idiom
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( each {|v| {k: ($v | do $keyfunc ), v: $v}}
| sort-by k
|
}
"Rosetta Code is a programming chrestomathy site" | split words | sort by key {str length}
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<pre>
╭───┬──────────────╮
│ 0 │ a │
│ 1 │ is │
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│ 6 │ chrestomathy │
╰───┴──────────────╯
</pre>
=={{header|Perl}}==
<syntaxhighlight lang="perl">#!/usr/bin/perl
use strict; # https://rosettacode.org/wiki/Decorate-sort-undecorate_idiom
use warnings;
use List::AllUtils qw( nsort_by );
my @list = ("Rosetta", "Code", "is", "a", "programming", "chrestomathy", "site");
print "@list\n";
my @sortedlist = nsort_by { length } @list;
print "@sortedlist\n";</syntaxhighlight>
{{out}}
<pre>
Rosetta Code is a programming chrestomathy site
a is Code site Rosetta programming chrestomathy
</pre>
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cached: ["a", "is", "Code", "site", "Rosetta", "programming", "chrestomathy"]
transform: ["a", "is", "Code", "site", "Rosetta", "programming", "chrestomathy"]
</pre>
=={{header|Sidef}}==
<syntaxhighlight lang="ruby">var str = "Rosetta Code is a programming chrestomathy site"
# Built-in
say str.split.sort_by{.len}
# Same thing explicitly
say str.split.map {|w| [w, w.len] }.sort{|a,b| a[1] <=> b[1] }.map { _[0] }
# Sort by word length, then lexical:
var str2 = str+" seven extra words added to this demo"
say str2.split.sort_by{|word| [word.len, word] }</syntaxhighlight>
{{out}}
<pre>
["a", "is", "Code", "site", "Rosetta", "programming", "chrestomathy"]
["a", "is", "Code", "site", "Rosetta", "programming", "chrestomathy"]
["a", "is", "to", "Code", "demo", "site", "this", "added", "extra", "seven", "words", "Rosetta", "programming", "chrestomathy"]
</pre>
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It's not specified how words of equal length are to be sorted. The standard sort() method used here (quicksort under the hood) is unstable and so the sort order for such words is not guaranteed.
<syntaxhighlight lang="
System.print(a.map { |e| [e, f.call(e)] } // decorate
.toList
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