Dictionary sorting problem?

<code>$a=array(2,1,4,7,1,4,1,9)
</code>

I want to get key/value, where key is the value and value is the number of times the value appears, as shown below:

<code>$b={2:1,1:3,4:2,7:1,9:1}
</code>

There are many elements in $a. How to solve this problem with the fewest loops?

Reply content:

<code>$a=array(2,1,4,7,1,4,1,9)
</code>

I want to get key/value, where key is the value and value is the number of times the value appears, as shown below:

<code>$b={2:1,1:3,4:2,7:1,9:1}
</code>

There are many elements in $a. How to solve this problem with the fewest loops?

<code class="php">// 直接用函数
>>> array_count_values($a)
=> [
     2 => 1,
     1 => 3,
     4 => 2,
     7 => 1,
     9 => 1,
   ]
</code>

<code>$b = [];
foreach ($a as $i) {
   $b[$i] =  isset($b[$i]) ? $b[$i] + 1 : 0;
}</code>

Loop once