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module · Ruby 3.1

Enumerable

61 instance methods

What’s Here

Module Enumerable provides methods that are useful to a collection class for:

These methods return information about the Enumerable other than the elements themselves:

include?, member?: Returns true if self == object, false otherwise.
all?: Returns true if all elements meet a specified criterion; false otherwise.
any?: Returns true if any element meets a specified criterion; false otherwise.
none?: Returns true if no element meets a specified criterion; false otherwise.
one?: Returns true if exactly one element meets a specified criterion; false otherwise.
count: Returns the count of elements, based on an argument or block criterion, if given.
tally: Returns a new Hash containing the counts of occurrences of each element.

These methods return entries from the Enumerable, without modifying it:

Leading, trailing, or all elements:

Minimum and maximum value elements:

min: Returns the elements whose values are smallest among the elements, as determined by <=> or a given block.
max: Returns the elements whose values are largest among the elements, as determined by <=> or a given block.
minmax: Returns a 2-element Array containing the smallest and largest elements.
min_by: Returns the smallest element, as determined by the given block.
max_by: Returns the largest element, as determined by the given block.
minmax_by: Returns the smallest and largest elements, as determined by the given block.

Groups, slices, and partitions:

group_by: Returns a Hash that partitions the elements into groups.
partition: Returns elements partitioned into two new Arrays, as determined by the given block.
slice_after: Returns a new Enumerator whose entries are a partition of self, based either on a given object or a given block.
slice_before: Returns a new Enumerator whose entries are a partition of self, based either on a given object or a given block.
slice_when: Returns a new Enumerator whose entries are a partition of self based on the given block.
chunk: Returns elements organized into chunks as specified by the given block.
chunk_while: Returns elements organized into chunks as specified by the given block.

These methods return elements that meet a specified criterion.

find, detect: Returns an element selected by the block.
find_all, filter, select: Returns elements selected by the block.
find_index: Returns the index of an element selected by a given object or block.
reject: Returns elements not rejected by the block.
uniq: Returns elements that are not duplicates.

These methods return elements in sorted order.

each_entry: Calls the block with each successive element (slightly different from each).
each_with_index: Calls the block with each successive element and its index.
each_with_object: Calls the block with each successive element and a given object.
each_slice: Calls the block with successive non-overlapping slices.
each_cons: Calls the block with successive overlapping slices. (different from each_slice).
reverse_each: Calls the block with each successive element, in reverse order.

map, collect: Returns objects returned by the block.
filter_map: Returns truthy objects returned by the block.
flat_map, collect_concat: Returns flattened objects returned by the block.
grep: Returns elements selected by a given object or objects returned by a given block.
grep_v: Returns elements selected by a given object or objects returned by a given block.
reduce, inject: Returns the object formed by combining all elements.
sum: Returns the sum of the elements, using method +++.
zip: Combines each element with elements from other enumerables; returns the n-tuples or calls the block with each.
cycle: Calls the block with each element, cycling repeatedly.

To use module Enumerable in a collection class:

Include it:

Example
```
include Enumerable
```
Implement method each which must yield successive elements of the collection. The method will be called by almost any Enumerable method.

Example:

Example

class Foo
  include Enumerable
  def each
    yield 1
    yield 1, 2
    yield
  end
end
Foo.new.each_entry{ |element| p element }

Output:

Example

1
[1, 2]
nil

Some Ruby classes include Enumerable:

Virtually all methods in Enumerable call method each in the including class:

The example code snippets for the Enumerable methods:

Always show the use of one or more Array-like classes (often Array itself).
Sometimes show the use of a Hash-like class. For some methods, though, the usage would not make sense, and so it is not shown. Example: tally would find exactly one of each Hash entry.