如何计算一个数组来填充另一个数组？

Question

I have one array stores grade names, with grade value as key and grade name as value:

$labels=array(1=>'Insufficient',2=>'Sufficient',3=>'Satisfactory',4=>'Good',5=>'Excellent' );

Then, there's another array stores all record of people who gained a grade, with user_id as key and grade value as value:

$grades = array( 123 = > 1, 456 => 5 , 789 = > 3);

Now I want to count the record under each grade-- grade-1 => 5 users, grade-2=>6 users, in the form like this:

array(1=>5, 2=>6, 3=>2, 4=>2, 5=>1);

I tried this and got errors of Undefined offset:

$result = array();

for($i=1;$i<=5;++$i)
{
    foreach($grades as $user_id=>$user_grade)
    {
        $result[$i] = ( $user_grade == $i ) ? $result[$i]+1 : $result[$i];
    }
}

How to get an result array of counting how many user under each grade?

Answer 1

Sounds like array_count_values() would do the trick.

e.g.

<?php
$grades = array ( // this array contains no value "1"
   68 => 4, 138 => 4, 189 => 2, 255 => 4,
  297 => 3, 366 => 2, 425 => 4, 465 => 3,
  489 => 5, 580 => 4, 646 => 4, 704 => 5,
  784 => 2, 811 => 4, 897 => 4, 974 => 5,
  1006 => 2, 1093 => 2, 1189 => 2, 1222 => 4
);

$cnt = array_count_values($grades);
$cnt += array(1=>0,0,0,0,0);
ksort($cnt);

print_r($cnt);

prints

Array
(
    [1] => 0
    [2] => 6
    [3] => 2
    [4] => 9
    [5] => 3
)