The same functionality appears in different programming languages under different names. Here’s an attempt at gathering some interesting distinctions.

Remove/keep elements matching predicate

Plain old filter:

• filter (what is the opposite though?)
• select + reject (Smalltalk, Ruby)
• partition (combines both; Ruby, Rust)

Filter, mutates original:

• keep_if, delete_if (Ruby)

Filter until predicate fails:

• drop_while, take_while (Ruby)
• skip_while, take_while (Rust)

Find single element matching predicate

• find (Ruby, Rust)
• detect (Smalltalk)

Map elements

This applies a map to the elements of an array.

• map
• collect (Smalltalk, Ruby)
• transform (Ruby, e.g. transform_keys and transform_values)

Check equality

Equality is a can of worms.

• =
• ==
• ===
• ====
• eql?(other)
• isEqual(other)
• equals
• equal?

Check inclusion

• include?
• includes?
• contain?
• contains?

Number of array elements

• count
• size
• length