Exercise2 - Skill level ordered by the number of people, with the skill that most people have coming first.

index.php

<?php

$input = [
    [
        "id"=> 1,
        "name"=> "Teri Dalby",
        "skill"=> "Mountainbiking",
        "skillLevel"=> 10
    ],
    [
        "id"=> 2,
        "name"=> "Briana Durham",
        "skill"=> "Mountainbiking",
        "skillLevel"=> 3
    ],
    [
        "id"=> 3,
        "name"=> "Ellie Choi",
        "skill"=> "Skiing",
        "skillLevel"=> 7
    ],
    [
        "id"=> 4,
        "name"=> "Teri Dalby",
        "skill"=> "Paragliding",
        "skillLevel"=> 6
    ],
    [
        "id"=> 5,
        "name"=> "Briana Durham",
        "skill"=> "Paragliding",
        "skillLevel"=> 5
    ],
    [
        "id"=> 6,
        "name"=> "Cian Galert",
        "skill"=> "Mountainbiking",
        "skillLevel"=> 5
    ]
];

function printTopLevelSkills(array $input) {
    $results = [];
    foreach ($input as $entry) {
        if (! array_key_exists($entry['skill'], $results)) {
            // bootstrap
            $results[$entry['skill']] = ['people' => 0, 'level' => 0];
        }

        // populate
        $results[$entry['skill']] = [
            'people' =>  $results[$entry['skill']]['people'] + 1,
            'level' =>  $results[$entry['skill']]['level'] + $entry['skillLevel']
        ];
    }

    // compute average
    $average = array_map(function ($result, $key) {
        return ['skill' => $key, 'people' => $result['people'], 'average' => $result['level'] / $result['people']];
    }, $results, array_keys($results));


    // sort
    usort($average, function ($a, $b) {
        return $a['people'] < $b['people'];
    });

    return $average;
}

$results = printTopLevelSkills($input);

// display results
foreach ($results as $result) {
    echo sprintf(
        "%s (%s=>%d, %s=> %d)\n",
        $result['skill'],
        'people',
        $result['people'],
        'average level',
        $result['average']
    );
}

/**
Expected output=>

Mountainbiking (people=> 3, average level=> 6)
Paragliding (people=> 2, average level=> 5.5)
Skiing (people=> 1, average level=> 7)
*/

main.ts

const input = [
    {
        "id": 1,
        "name": "Teri Dalby",
        "skill": "Mountainbiking",
        "skillLevel": 10
    },
    {
        "id": 2,
        "name": "Briana Durham",
        "skill": "Mountainbiking",
        "skillLevel": 3
    },
    {
        "id": 3,
        "name": "Ellie Choi",
        "skill": "Skiing",
        "skillLevel": 7
    },
    {
        "id": 4,
        "name": "Teri Dalby",
        "skill": "Paragliding",
        "skillLevel": 6
    },
    {
        "id": 5,
        "name": "Briana Durham",
        "skill": "Paragliding",
        "skillLevel": 5
    },
    {
        "id": 6,
        "name": "Cian Galert",
        "skill": "Mountainbiking",
        "skillLevel": 5
    }
] as const;

type Person = {
    id: number;
    name: string;
    skill: string;
    skillLevel: number;
};

type SkillSummary = {
    skill: string;
    people: number;
    average: number;
};

function printTopLevelSkills(input: Person[]): SkillSummary[] {
    const results: Record<string, { people: number; level: number }> = {};

    input.forEach(entry => {
        if (!results[entry.skill]) {
            results[entry.skill] = { people: 0, level: 0 };
        }

        results[entry.skill].people += 1;
        results[entry.skill].level += entry.skillLevel;
    });

    const average: SkillSummary[] = Object.keys(results).map(skill => ({
        skill,
        people: results[skill].people,
        average: results[skill].level / results[skill].people
    }));

    // Sort by number of people descending
    average.sort((a, b) => b.people - a.people);

    return average;
}

const results = printTopLevelSkills(input);

// Display results
results.forEach(result => {
    console.log(`${result.skill} (people=> ${result.people}, average level=> ${result.average})`);
});