PHP sortについて sort(), asort(), ksort()

#各ソートの実施例

例）

<?php 
$arr['aka'] = 'ichigo';
$arr['red']= 'apple';
$arr['yellow'] = 'banana';
$arr['green'] = 'melon';

//var_dump($arr);
//結果
/*
array(4) {
  ["aka"]=>
  string(6) "ichigo"
  ["red"]=>
  string(5) "apple"
  ["yellow"]=>
  string(6) "banana"
  ["green"]=>
  string(5) "melon"
}*/


sort($arr);
// var_dump($arr);//値を元にソート（昇順・キーが数値になる）
//結果
/*
array(4) {
  [0]=>
  string(5) "apple"
  [1]=>
  string(6) "banana"
  [2]=>
  string(6) "ichigo"
  [3]=>
  string(5) "melon"
}
*/

$arr2['aka'] = 'ichigo';
$arr2['red']= 'apple';
$arr2['yellow'] = 'banana';
$arr2['green'] = 'melon';

//var_dump($arr);
//結果
/*
array(4) {
  ["aka"]=>
  string(6) "ichigo"
  ["red"]=>
  string(5) "apple"
  ["yellow"]=>
  string(6) "banana"
  ["green"]=>
  string(5) "melon"
}*/
asort($arr2);//値を元にソート（昇順）
var_dump($arr2);
/*
array(4) {
  ["red"]=>
  string(5) "apple"
  ["yellow"]=>
  string(6) "banana"
  ["aka"]=>
  string(6) "ichigo"
  ["green"]=>
  string(5) "melon"
}
*/

$arr3['aka'] = 'ichigo';
$arr3['red']= 'apple';
$arr3['yellow'] = 'banana';
$arr3['green'] = 'melon';

//var_dump($arr);
//結果
/*
array(4) {
  ["aka"]=>
  string(6) "ichigo"
  ["red"]=>
  string(5) "apple"
  ["yellow"]=>
  string(6) "banana"
  ["green"]=>
  string(5) "melon"
}*/

ksort($arr3);//キーを基準にソート（昇順）
var_dump($arr3);
/*
array(4) {
  ["aka"]=>
  string(6) "ichigo"
  ["green"]=>
  string(5) "melon"
  ["red"]=>
  string(5) "apple"
  ["yellow"]=>
  string(6) "banana"
}
*/