Group SQL data by JSON arrays - php

Question

I am working on a page for teachers that shows results of students' performance on a test.
To display a graph I want to use Highcharts JavaScript library.
So far I have a PHP script using PDO to create JSON data that later can be fed to Highcharts from a different page.
My problem:
How do I group all data from the same student in an array? See the last example for what I wish to achieve. Also: I wish to enclose all data in an overarching JSON array.
I want this:
[{
"student": "Andreas",
"level" : [4, 3]
}, {
"student": "Eivind",
"level" : [4, 5]
}, {
"student": "Ole",
"level" : [4, 3]
}]
This is what my PHP looks like:
<?php
require("config.inc.php");
$school = $_GET["school"];
$class = $_GET["class"];
//initial query
$query = 'SELECT student, taskid, level FROM task
WHERE school=' . '"' . $school . '"' . ' AND class=' . '"' . $class . '" ORDER BY student';
//execute query
try {
$stmt = $db->prepare($query);
$result = $stmt->execute();
}
catch (PDOException $ex) {
$response["success"] = 0;
$response["message"] = "Database Error!";
die(json_encode($response));
}
// Finally, we can retrieve all of the found rows into an array using fetchAll
$rows = $stmt->fetchAll();
if ($rows) {
$response["posts"] = array();
foreach ($rows as $row) {
$post = array();
$post["student"] = $row["student"];
$post["level"] = $row["level"];
//update our repsonse JSON data
array_push($response["posts"], $post);
}
// echoing JSON response
echo json_encode($response, JSON_NUMERIC_CHECK);
} else {
$response["success"] = 0;
$response["message"] = "No Post Available!";
die(json_encode($response));
}
?>
This is what I get from the PHP:
{
"posts": [
{
"student": "Andreas",
"level": 4
},
{
"student": "Andreas",
"level": 3
},
{
"student": "Eivind",
"level": 4
},
{
"student": "Eivind",
"level": 5
},
{
"student": "Ole",
"level": 4
},
{
"student": "Ole",
"level": 3
}
]
}

Answer 1

var data=[
{ "category" : "Search Engines", "hits" : 5, "bytes" : 50189 },
{ "category" : "Content Server", "hits" : 1, "bytes" : 17308 },
{ "category" : "Content Server", "hits" : 1, "bytes" : 47412 },
{ "category" : "Search Engines", "hits" : 1, "bytes" : 7601 },
{ "category" : "Business", "hits" : 1, "bytes" : 2847 },
{ "category" : "Content Server", "hits" : 1, "bytes" : 24210 },
{ "category" : "Internet Services", "hits" : 1, "bytes" : 3690 },
{ "category" : "Search Engines", "hits" : 6, "bytes" : 613036 },
{ "category" : "Search Engines", "hits" : 1, "bytes" : 2858 }
];
var res = alasql('SELECT category, sum(hits) AS hits, sum(bytes) as bytes \
FROM ? \
GROUP BY category \
ORDER BY bytes DESC',[data]);
You will get output as:
[{"category":"Search Engines","hits":13,"bytes":673684},
{"category":"Content Server","hits":3,"bytes":88930},
{"category":"Internet Services","hits":1,"bytes":3690},
{"category":"Business","hits":1,"bytes":2847}]

Answer 2

You can construct an array like this pretty easily by using the student names as array keys. After you have built the array, you can use array_values to convert the string keys back to numeric keys.
...
if ($rows) {
foreach ($rows as $row) {
$posts[$row['student']]['student'] = $row['student'];
$posts[$row['student']]['level'][] = $row['level'];
}
$response = array_values($posts);
echo json_encode($response, JSON_NUMERIC_CHECK);
} else { ...
This should give you the following $response:
[
{
"student": "Andreas",
"level": [4, 3]
},
{
"student": "Eivind",
"level": [4, 5]
},
{
"student": "Ole",
"level": [4, 3]
}
]

Answer 3

In php you can do this:
In your foreach
foreach ($rows as $row) {
$post = array();
$post["student"] = $row["student"];
$post["level"] = $row["level"];
//update our repsonse JSON data
array_push($response["posts"], $post);
}
you need to do something like this:
<?php
$response = array();
$response["posts"] = array();
$students = array("student1", "student2", "student3", "student1");
$tempArray = array();
foreach ($students as $student) {
$lvl = 1;
if(!isset($tempArray[$student])){
$tempArray[$student] = array("name" => $student, "level" => array($lvl));
}
else{
$tempArray[$student]["level"][] = $lvl;
}
}
// add it to the array
$response["posts"] = $tempArray;
// encode array
$response = json_encode($response);
echo "<br><br><br> ";
// example
// decode and make it a array for easier looping.
$response = (array)json_decode($response);
$responsePosts = (array) $response["posts"];
// foreach post
foreach($response["posts"] as $keyP => $valueP){
// convert to array same as above
$valueP = (array) $valueP;
// key that is kinda useless but made it the student name so i can easily see if it already exists
echo "key :".$keyP." <br />";
// name of the student
echo "name :".$valueP["name"]." <br />";
// all the levels
echo "levels: ";
foreach($valueP["level"] as $lvl){
echo $lvl." ";
}
echo "<br /><br />";
}
?>
This should work. Atm i use the student name as a key to see if it already exists otherwise you need to loop through all the arrays and do a "name" === $student most likely.
No push is required.