Returns a new array containing each element in self that is #eql? to at least one element in each of the given other_arrays; duplicates are omitted:

[0, 0, 1, 1, 2, 3].intersection([0, 1, 2], [0, 1, 3]) # => [0, 1]

Each element must correctly implement method #hash.

Order from self is preserved:

[0, 1, 2].intersection([2, 1, 0]) # => [0, 1, 2]

Returns a copy of self if no arguments are given.

Related: see Methods for Combining.

String#partition

Returns a 3-element array of substrings of self.

Matches a pattern against self, scanning from the beginning. The pattern is:

string_or_regexp itself, if it is a Regexp.
Regexp.quote(string_or_regexp), if string_or_regexp is a string.

If the pattern is matched, returns pre-match, first-match, post-match:

'hello'.partition('l')      # => ["he", "l", "lo"]
'hello'.partition('ll')     # => ["he", "ll", "o"]
'hello'.partition('h')      # => ["", "h", "ello"]
'hello'.partition('o')      # => ["hell", "o", ""]
'hello'.partition(/l+/)     #=> ["he", "ll", "o"]
'hello'.partition('')       # => ["", "", "hello"]
'тест'.partition('т')       # => ["", "т", "ест"]
'こんにちは'.partition('に')  # => ["こん", "に", "ちは"]

If the pattern is not matched, returns a copy of self and two empty strings:

'hello'.partition('x') # => ["hello", "", ""]

String#rpartition

Returns a 3-element array of substrings of self.

Matches a pattern against self, scanning backwards from the end. The pattern is:

string_or_regexp itself, if it is a Regexp.
Regexp.quote(string_or_regexp), if string_or_regexp is a string.

If the pattern is matched, returns pre-match, last-match, post-match:

'hello'.rpartition('l')      # => ["hel", "l", "o"]
'hello'.rpartition('ll')     # => ["he", "ll", "o"]
'hello'.rpartition('h')      # => ["", "h", "ello"]
'hello'.rpartition('o')      # => ["hell", "o", ""]
'hello'.rpartition(/l+/)     # => ["hel", "l", "o"]
'hello'.rpartition('')       # => ["hello", "", ""]
'тест'.rpartition('т')       # => ["тес", "т", ""]
'こんにちは'.rpartition('に')  # => ["こん", "に", "ちは"]

If the pattern is not matched, returns two empty strings and a copy of self:

'hello'.rpartition('x') # => ["", "", "hello"]

Set#intersection

No documentation available

Enumerable#partition

With a block given, returns an array of two arrays:

The first having those elements for which the block returns a truthy value.
The other having all other elements.

Examples:

p = (1..4).partition {|i| i.even? }
p # => [[2, 4], [1, 3]]
p = ('a'..'d').partition {|c| c < 'c' }
p # => [["a", "b"], ["c", "d"]]
h = {foo: 0, bar: 1, baz: 2, bat: 3}
p = h.partition {|key, value| key.start_with?('b') }
p # => [[[:bar, 1], [:baz, 2], [:bat, 3]], [[:foo, 0]]]
p = h.partition {|key, value| value < 2 }
p # => [[[:foo, 0], [:bar, 1]], [[:baz, 2], [:bat, 3]]]

With no block given, returns an Enumerator.

Related: Enumerable#group_by.

Gem::configuration

The standard configuration object for gems.

Gem::configuration=

Use the given configuration object (which implements the ConfigFile protocol) as the standard configuration object.

DateTime#second_fraction

Returns the fractional part of the second in range (Rational(0, 1)…Rational(1, 1)):

DateTime.new(2001, 2, 3, 4, 5, 6.5).sec_fraction # => (1/2)

TracePoint#instruction_sequence

Returns the compiled instruction sequence represented by a RubyVM::InstructionSequence instance on the :script_compiled event.

Note that this method is CRuby-specific.