Arrays & Array Methods (map, filter, reduce)

What data transformation is being performed?

const records = [
  { id: 1, value: 10 },
  { id: 2, value: 20 },
  { id: 1, value: 30 }
];
const merged = records.reduce((acc, curr) => {
  acc[curr.id] = (acc[curr.id] || 0) + curr.value;
  return acc;
}, {});

Counting occurrences
Finding duplicates
Merging values by ID
This reduces records to sum values by ID: 1) Creates object accumulator for results, 2) Uses ID as key for grouping, 3) Initializes value if not exists, 4) Adds current value to accumulated sum, 5) Results in {1: 40, 2: 20}, 6) Handles multiple records with same ID, 7) Common pattern for data aggregation, 8) Useful for grouping and summarizing data.
Sorting by ID

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