PHP: How to Group and Sum Up in Array

Question

This is my array

array(
      ['studentId'=>"M100030","isbn"=>"0199535566",'price'=>"15.00"],
      ['studentId'=>"M100030","isbn"=>"0199535566",'price'=>"13.50"],
      ['studentId'=>"M100030","isbn"=>"0143105426",'price'=>"20.00"],
      ['studentId'=>"M100035","isbn"=>"1604501480",'price'=>"21.00"],
      ['studentId'=>"M100035","isbn"=>"1604501480",'price'=>"23.00"],
      ['studentId'=>"M100035","isbn"=>"0199535566",'price'=>"14.00"],
      ['studentId'=>"M103233","isbn"=>"0061964360",'price'=>"18.50"],
    );

I want to group the studentId and isbn then sum up the price to JSON

{
   "M100030":{
      "0199535566":{
         "amount":"28.50"
      },
      "0143105426":{
         "amount":"20.00"
      }
   },
   "M100035":{
      "1604501480":{
         "amount":"44.00"
      },
      "0199535566":{
         "amount":"14.00"
      }
   },
   "M103233":{
      "0061964360":{
         "amount":"18.50"
      }
   }
}

The method I tried so far to group the studentId and isbn, but not able to get the expected result. Anyone can correct my code?

foreach ($check['rentout'] as $key=> $values)
{

    $keys = $values['studentId'];
    if (!array_key_exists($keys,$trx)){
      $trx[$keys] = array('isbn'=>$values['isbn'],'amount'=>$values['price']);
    }else{
      $trx[$keys]['amount'] = $trx[$keys]['amount']+$values['price'];
    }

}

Since you're doing arithmetic with decimals, you should take a look at What Every Programmer Should Know About Floating-Point Arithmetic — Definitely not Rafal
– Definitely not Rafal, Commented May 26, 2021 at 14:51

TAHER El Mehdi · Accepted Answer · 2021-05-26 14:47:26Z

$students = array(
      ['studentId'=>"M100030","isbn"=>"0199535566",'price'=>"15.00"],
      ['studentId'=>"M100030","isbn"=>"0199535566",'price'=>"13.50"],
      ['studentId'=>"M100030","isbn"=>"0143105426",'price'=>"20.00"],
      ['studentId'=>"M100035","isbn"=>"1604501480",'price'=>"21.00"],
      ['studentId'=>"M100035","isbn"=>"1604501480",'price'=>"23.00"],
      ['studentId'=>"M100035","isbn"=>"0199535566",'price'=>"14.00"],
      ['studentId'=>"M103233","isbn"=>"0061964360",'price'=>"18.50"],
    );

I Created variable $res and I looped over $students and get the $student_id and do a test if there is no isbn for this student, If So set their amount to the initial value, and loop again if we find it again accumulate its prices to amount, and do this again and again to all students in the array.

$res = [];
foreach ($students as $key => $student) {
    $student_id = $student['studentId'];
    if (!isset($res[$student_id][$student["isbn"]])){
      $res[$student_id][$student["isbn"]]["amount"] = $student['price'];
    }else{
        $res[$student_id][$student["isbn"]]["amount"] += $student['price'];
    }
}

echo "<pre>";
echo json_encode($res, JSON_PRETTY_PRINT);

Print(as excpected)

{
    "M100030": {
        "0199535566": {
            "amount": 28.5
        },
        "0143105426": {
            "amount": "20.00"
        }
    },
    "M100035": {
        "1604501480": {
            "amount": 44
        },
        "0199535566": {
            "amount": "14.00"
        }
    },
    "M103233": {
        "0061964360": {
            "amount": "18.50"
        }
    }
}

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