Aggregating with reduce()

The reduce() method processes an array to produce a single value. It's powerful for summing, grouping, and restructuring data.

Basic Reduce

Reducing Objects

Grouping Data

Counting Occurrences

Building New Structures

Exercise: Sum Values

Exercise: Group by Category

Exercise: Count Items

Key Points

• reduce() transforms array to any single value
• Parameters: callback(accumulator, current), initialValue
• Always provide an initial value
• Use for sums, groups, counts, lookups
• Can replace many filter + map chains