Extract array entries to fit perfectly fit cases - php

Question

I am building a student application where I need to find what files are the best match for the students based on the files that have number of the semesters they need to cover.
Each student is uploading a file where they select a number of semesters that are covered. Let's say file X has semester 1 and 2, file Y has semesters 1, 3, 4 and so on.
The only order here is the ascending order. The number of selected semesters can be random (1 or 1,2,3 or 3,4 or or 2,5,6 or 1,2,5,6,8 or any combination of this kind).
What i need to achieve is to get the least number of files covering the maximum amount of semesters taking into account the smaller semester to be covered.
In my example a special case is required semesters 5 where I could return files 1, 2, 3, 4 because all this contains semesters to be covered but this is not what I am looking for. Instead i need to get file 3 and 4 which covers perfectly the case.
I am providing files where each file is covering a number of semesters like this:
Student files in the following files:
file 1 covers semester: array(3)
file 2 covers semester: array(3,4)
file 3 covers semester: array(1,2)
file 4 covers semester: array(3,4,5,6)
$aUserFiles = [
0 => [
'file' => 'file 1',
'semesters' => [
3
]
],
1 => [
'file' => 'file 2',
'semesters' => [
3,4
]
],
2 => [
'file' => 'file 3',
'semesters' => [
1,2
]
],
3 => [
'file' => 'file 4',
'semesters' => [
3,4,5,6
]
]
];
Semesters that needs to be covered and expected results:
Option 1: number of semesters required: 5.
Expected result: file 3, file 4
$aResult = [
0 => [
'file' => 'file 3',
'semesters' => [
1,2
]
],
1 => [
'file' => 'file 4',
'semesters' => [
3,4,5,6
]
]
];
Option 2: number of semesters required: 2.
Expected result: file 3
$aResult = [
0 => [
'file' => 'file 3',
'semesters' => [
1,2
]
]
];
Option 3: number of semesters required: 4.
Expected result: file 3, file 2
Option 4: number of semesters required: 3.
Expected result: file 3, file 1

Answer 1

You can do something like this:
$requiredSemesters = 3; // Your input
$indicators = [];
$result = [];
foreach ($aUserFiles as $key => $file) {
$first = $file['semesters'][0];
$last = $file['semesters'][count($file['semesters']) - 1];
$filesInRangeCount = count(array_intersect($file['semesters'], range(1, $requiredSemesters)));
if (!isset($indicators[$first]) || $indicators[$first]['range'] < $filesInRangeCount) {
$indicators[$first] = ["key" => $key, "max" => $last, "range" => $filesInRangeCount];
}
}
ksort($indicators);
$result = [];
$max = 0;
foreach ($indicators as $indicator) {
if ($max >= $requiredSemesters) {
break;
}
$result[] = $aUserFiles[$indicator['key']];
$max = $indicator["max"];
}
print_r($result);
Demo: https://3v4l.org/ZfDLo
Explanation:
I make a new array and insert the values grouped by minimum value (first number since your arrays are ordered). In that process I make sure to leave only the file with highest number of overlap with your input (1-input) and (first number - last number). Now I sort the grouped array, and iterate. All I need to do now is to add the files until I reach the maximum number which is the given input.