Iterators & Enumerators in Ruby

Use Ruby's powerful iterators like map, select, reject, reduce, each_with_object, and lazy enumerators.

Ruby's Iteration Model

In Ruby, iteration is built on blocks. Methods like each, map, and select accept a block and call it for each element. This is more expressive than manual for loops.

1. each — Basic Iteration

Iterate over any collection.

2. each_with_index

Access index alongside element.

3. times, upto, downto

Numeric iteration shortcuts.

Transforming Collections

map (also called collect) transforms each element. flat_map maps and flattens. zip combines arrays element-by-element.

1. map / collect

Transform each element.

2. flat_map

Map and flatten one level.

3. zip

Combine multiple arrays element-by-element.

Filtering Collections

select (alias filter) keeps elements matching a condition. reject keeps those that do NOT match. find returns the first match.

1. select / filter

Keep elements matching condition.

2. reject

Exclude elements matching condition.

3. find / detect

Return first matching element.

Reducing & Aggregating

reduce (also inject) folds a collection into a single value. Ruby also provides convenient built-ins like sum, min, max, count.

1. reduce / inject

Fold collection into single value.

2. reduce with Symbol Shorthand

Pass operator as symbol.

3. Built-in Aggregation Methods

sum, min, max, count.

Grouping & Sorting

Ruby provides high-level grouping and sorting methods that work with any Enumerable.

1. group_by

Group elements by a computed key.

2. sort_by

Sort by a computed key.

3. each_slice and each_cons

Process elements in batches or windows.

4. tally

Count occurrences of each element.

Enumerator & Lazy Evaluation

Ruby's Enumerator class lets you create custom iterators. Calling .lazy on any Enumerable gives a lazy chain that processes elements on demand — ideal for large or infinite sequences.

1. Custom Enumerator with Enumerator.new

Build a custom iterator.

2. Lazy Enumerator

Process only what you need.

3. each_with_object

Build an object while iterating.