Practice Questions — Advanced Array and Object Patterns

const students = [
  { name: "Aarav", scores: { maths: 95, science: 88, english: 92 } },
  { name: "Priya", scores: { maths: 78, science: 95, english: 85 } },
  { name: "Rohan", scores: { maths: 82, science: 76, english: 80 } }
];

const withAvg = students.map(function(s) {
  const vals = Object.values(s.scores);
  const avg = vals.reduce(function(sum, v) { return sum + v; }, 0) / vals.length;
  return { name: s.name, average: Math.round(avg * 10) / 10 };
});

const topper = withAvg.reduce(function(best, s) {
  return s.average > best.average ? s : best;
});
console.log("Topper:", topper.name, "(Avg:", topper.average + ")");

const above90 = students.filter(function(s) {
  return Object.values(s.scores).some(function(v) { return v > 90; });
});
console.log("Above 90:", above90.map(function(s) { return s.name; }).join(", "));

function wordFrequency(text) {
  const words = text.toLowerCase().split(/\s+/);
  const freq = words.reduce(function(acc, word) {
    acc[word] = (acc[word] || 0) + 1;
    return acc;
  }, {});
  return Object.entries(freq)
    .sort(function(a, b) { return b[1] - a[1]; })
    .map(function([word, count]) { return word + ": " + count; })
    .join(", ");
}
console.log(wordFrequency("the cat sat on the mat the cat"));

const cart = [
  { name: "Book", price: 300, qty: 2, category: "Study" },
  { name: "Pen", price: 25, qty: 10, category: "Study" },
  { name: "Mouse", price: 500, qty: 1, category: "Electronics" }
];

const total = cart.reduce(function(sum, i) { return sum + i.price * i.qty; }, 0);
console.log("Total: Rs", total);

const byCat = cart.reduce(function(acc, i) {
  acc[i.category] = (acc[i.category] || 0) + i.price * i.qty;
  return acc;
}, {});

const topCat = Object.entries(byCat).sort(function(a, b) { return b[1] - a[1]; })[0];
console.log("Most expensive category:", topCat[0]);

const sorted = [...cart].sort(function(a, b) {
  return (b.price * b.qty) - (a.price * a.qty);
}).map(function(i) { return i.name + ": Rs " + (i.price * i.qty); });
console.log("By value:", sorted);

const players = [
  { name: "Aarav", score: 920, wins: 12 },
  { name: "Priya", score: 950, wins: 15 },
  { name: "Rohan", score: 920, wins: 14 },
  { name: "Meera", score: 880, wins: 10 }
];

const ranked = [...players].sort(function(a, b) {
  if (b.score !== a.score) return b.score - a.score;
  return b.wins - a.wins;
});

function getTopN(n) {
  return ranked.slice(0, n);
}

function getRank(name) {
  return ranked.findIndex(function(p) { return p.name === name; }) + 1;
}

function topAvg(n) {
  const top = getTopN(n);
  return top.reduce(function(s, p) { return s + p.score; }, 0) / top.length;
}

console.log("Leaderboard:");
ranked.forEach(function(p, i) {
  console.log((i+1) + ". " + p.name + " - " + p.score + " (" + p.wins + " wins)");
});
console.log("Aarav rank:", getRank("Aarav"));
console.log("Top 3 avg:", topAvg(3).toFixed(1));

const users = [
  { name: "Aarav", address: { city: "Delhi" }, posts: [{t: "a"}, {t: "b"}, {t: "c"}] },
  { name: "Priya", address: { city: "Delhi" }, posts: [{t: "d"}, {t: "e"}, {t: "f"}, {t: "g"}, {t: "h"}] },
  { name: "Rohan", address: { city: "Mumbai" }, posts: [{t: "i"}] },
  { name: "Meera", address: { city: "Delhi" }, posts: [{t: "j"}, {t: "k"}, {t: "l"}, {t: "m"}] }
];

const delhiUsers = users.filter(function(u) { return u.address.city === "Delhi"; });
const allPosts = delhiUsers.flatMap(function(u) { return u.posts; });
const postCounts = delhiUsers.map(function(u) {
  return { name: u.name, count: u.posts.length };
}).sort(function(a, b) { return b.count - a.count; });

const summary = {
  delhiUsers: delhiUsers.length,
  totalPosts: allPosts.length,
  mostActive: postCounts[0].name + " (" + postCounts[0].count + " posts)"
};
console.log(summary);

function objectDiff(oldObj, newObj) {
  const oldKeys = Object.keys(oldObj);
  const newKeys = Object.keys(newObj);
  
  const added = Object.fromEntries(
    newKeys.filter(function(k) { return !oldKeys.includes(k); })
    .map(function(k) { return [k, newObj[k]]; })
  );
  
  const removed = Object.fromEntries(
    oldKeys.filter(function(k) { return !newKeys.includes(k); })
    .map(function(k) { return [k, oldObj[k]]; })
  );
  
  const changed = Object.fromEntries(
    oldKeys.filter(function(k) {
      return newKeys.includes(k) && oldObj[k] !== newObj[k];
    }).map(function(k) {
      return [k, { from: oldObj[k], to: newObj[k] }];
    })
  );
  
  return { added: added, removed: removed, changed: changed };
}

const diff = objectDiff(
  { name: "Aarav", age: 15, city: "Delhi" },
  { name: "Aarav", age: 16, school: "DPS" }
);
console.log(JSON.stringify(diff, null, 2));