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# Idiom #100 Sort by a comparator

Sort elements of array-like collection items, using a comparator c.

`#include <stdlib.h>`
```int c(const void *a,const void *b)
{
int x = *(const int *)a;
int y = *(const int *)b;

if (x < y) return -1;
if (x > y) return +1;
return 0;
}

int main(void)
{
int arr[]={1,6,3,7,2};
qsort(arr,sizeof(arr)/sizeof(*arr),sizeof(*arr),c);

return 0;
}
```
```with Ada.Containers.Vectors;
```type Integer_Comparator is not null access function (Left, Right : Integer) return Boolean;

package Integer_Vectors is new Vectors (Positive, Integer);
use Integer_Vectors;

procedure Sort_Using_Comparator (V : in out Vector; C : Integer_Comparator) is
package Vector_Sorting is new Generic_Sorting (C.all);
use Vector_Sorting;

begin
Sort (V);
end Sort_Using_Comparator;```
```#include <algorithm>
#include <vector>
#include <cassert>```
```struct is_less {
bool operator () (int a, int b){
return a < b;
}
};

int main(){
std::vector<int> items = {1337, 666, -666, 0, 0, 666, -666};
std::sort(items.begin(), items.end(), is_less());

std::vector<int> expected = {-666, -666, 0, 0, 666, 666, 1337};
assert(items.size() == expected.size());
for (size_t i = 0; i < items.size(); i++){
assert(items[i] == expected[i]);
}
return 0;
}
```
`import std.algorithm: sort;`
`items.sort!c;`
1
`Enum.sort(items, c)`
`lists:sort(C, List).`
`import "sort"`
```type ItemCSorter []Item
func (s ItemCSorter) Len() int           { return len(s) }
func (s ItemCSorter) Less(i, j int) bool { return c(s[i], s[j]) }
func (s ItemCSorter) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

func sortItems(items []Item) {
sorter := ItemCSorter(items)
sort.Sort(sorter)
}```
`import "sort"`
```sort.Slice(items, func(i, j int) bool {
return c(items[i], items[j])
})```
`import "sort"`
```type ItemsSorter struct {
items []Item
c     func(x, y Item) bool
}

func (s ItemsSorter) Len() int           { return len(s.items) }
func (s ItemsSorter) Less(i, j int) bool { return s.c(s.items[i], s.items[j]) }
func (s ItemsSorter) Swap(i, j int)      { s.items[i], s.items[j] = s.items[j], s.items[i] }

func sortItems(items []Item, c func(x, y Item) bool) {
sorter := ItemsSorter{
items,
c,
}
sort.Sort(sorter)
}```
`import Data.List`
`result = sortBy c items`
`items.sort(c);`
```import java.util.Collections;
import java.util.Comparator;```
`Collections.sort(items, c);`
```import java.util.Arrays;
import java.util.Comparator;```
`Arrays.sort(items, c);`
`table.sort(items,c)`
`uses classes;`
```with TList.Create do try
Sort(c);
finally
Free;
end;```
```sub c {
a <=> \$b;
}

my @result = sort c @items;

```
`items.sort(c)`
`items.sort!{|a,b| a-b }`
`items.sort!(&c)`
```fn main()
{
let c = |a: &u32,b: &u32|a.cmp(b);

let mut v = vec![1,7,5,2,3];
v.sort_by(c);
println!("{:#?}",v);
}
```

#### Idiom created by

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