role Baggy does QuantHash { }

A role for collections of weighted objects. See Bag, BagHash, and Mixy.

Methods

method new-from-pairs

method new-from-pairs(Baggy: *@pairs --> Baggy:D)

Constructs a Baggy objects from a list of Pair objects given as positional arguments:

say Mix.new-from-pairs: 'butter' => 0.22, 'sugar' => 0.1, 'sugar' => 0.02;
# OUTPUT: «Mix(butter(0.22) sugar(0.12))␤»

Note: be sure you aren't accidentally passing the Pairs as positional arguments; the quotes around the keys in the above example are significant.

method grab

multi method grab(Baggy:D: --> Any)
multi method grab(Baggy:D: $count --> Seq:D)

Like pick, a grab returns a random selection of elements, weighted by the values corresponding to each key. Unlike pick, it works only on mutable structures, e.g. BagHash. Use of grab on an immutable structure results in an X::Immutable exception. If * is passed as $count, or $count is greater than or equal to the total of the invocant, then total elements from the invocant are returned in a random sequence; i.e. they are returned shuffled.

Grabbing decrements the grabbed key's weight by one (deleting the key when it reaches 0). By definition, the total of the invocant also decreases by one, so the probabilities stay consistent through subsequent grab operations.

my $cars = ('Ford' => 2, 'Rover' => 3).BagHash;
say $cars.grab;                                   # OUTPUT: «Ford␤» 
say $cars.grab(2);                                # OUTPUT: «(Rover Rover)␤» 
say $cars.grab(*);                                # OUTPUT: «(Rover Ford)␤» 
 
my $breakfast = ('eggs' => 2, 'bacon' => 3).Bag;
say $breakfast.grab;
CATCH { default { put .^name, ': ', .Str } };
# OUTPUT: «X::Immutable: Cannot call 'grab' on an immutable 'Bag'␤»

method grabpairs

multi method grabpairs(Baggy:D: --> Any)
multi method grabpairs(Baggy:D: $count --> Seq:D)

Returns a Pair or a Seq of Pairs depending on the version of the method being invoked. Each Pair returned has an element of the invocant as its key and the element's weight as its value. Unlike pickpairs, it works only on mutable structures, e.g. BagHash. Use of grabpairs on an immutable structure results in an X::Immutable exception. If * is passed as $count, or $count is greater than or equal to the number of elements of the invocant, then all element/weight Pairs from the invocant are returned in a random sequence.

What makes grabpairs different from pickpairs is that the 'grabbed' elements are in fact removed from the invocant.

my $breakfast = (eggs => 2, bacon => 3).BagHash;
say $breakfast.grabpairs;                         # OUTPUT: «bacon => 3␤» 
say $breakfast;                                   # OUTPUT: «BagHash.new(eggs(2))␤» 
say $breakfast.grabpairs(1);                      # OUTPUT: «(eggs => 2)␤» 
say $breakfast.grabpairs(*);                      # OUTPUT: «()␤» 
 
my $diet = ('eggs' => 2, 'bacon' => 3).Bag;
say $diet.grabpairs;
CATCH { default { put .^name, ': ', .Str } };
# OUTPUT: «X::Immutable: Cannot call 'grabpairs' on an immutable 'Bag'␤»

method pick

multi method pick(Baggy:D: --> Any)
multi method pick(Baggy:D: $count --> Seq:D)

Like an ordinary list pick, but returns keys of the invocant weighted by their values, as if the keys were replicated the number of times indicated by the corresponding value and then list pick used. The underlying metaphor for picking is that you're pulling colored marbles out a bag. (For "picking with replacement" see roll instead). If * is passed as $count, or $count is greater than or equal to the total of the invocant, then total elements from the invocant are returned in a random sequence.

Note that each pick invocation maintains its own private state and has no effect on subsequent pick invocations.

my $breakfast = bag <eggs bacon bacon bacon>;
say $breakfast.pick;                              # OUTPUT: «eggs␤» 
say $breakfast.pick(2);                           # OUTPUT: «(eggs bacon)␤» 
 
say $breakfast.total;                             # OUTPUT: «4␤» 
say $breakfast.pick(*);                           # OUTPUT: «(bacon bacon bacon eggs)␤»

method pickpairs

multi method pickpairs(Baggy:D: --> Pair:D)
multi method pickpairs(Baggy:D: $count --> Seq:D)

Returns a Pair or a Seq of Pairs depending on the version of the method being invoked. Each Pair returned has an element of the invocant as its key and the element's weight as its value. The elements are 'picked' without replacement. If * is passed as $count, or $count is greater than or equal to the number of elements of the invocant, then all element/weight Pairs from the invocant are returned in a random sequence.

Note that each pickpairs invocation maintains its own private state and has no effect on subsequent pickpairs invocations.

my $breakfast = bag <eggs bacon bacon bacon>;
say $breakfast.pickpairs;                         # OUTPUT: «eggs => 1␤» 
say $breakfast.pickpairs(1);                      # OUTPUT: «(bacon => 3)␤» 
say $breakfast.pickpairs(*);                      # OUTPUT: «(eggs => 1 bacon => 3)␤»

method roll

multi method roll(Baggy:D: --> Any:D)
multi method roll(Baggy:D: $count --> Seq:D)

Like an ordinary list roll, but returns keys of the invocant weighted by their values, as if the keys were replicated the number of times indicated by the corresponding value and then list roll used. The underlying metaphor for rolling is that you're throwing $count dice that are independent of each other, which (in bag terms) is equivalent to picking a colored marble out your bag and then putting it back, and doing this $count times. In dice terms, the number of marbles corresponds to the number of sides, and the number of marbles of the same color corresponds to the number of sides with the same color. (For "picking without replacement" see pick instead).

If * is passed to $count, returns a lazy, infinite sequence of randomly chosen elements from the invocant.

my $breakfast = bag <eggs bacon bacon bacon>;
say $breakfast.roll;                                  # OUTPUT: «bacon␤» 
say $breakfast.roll(3);                               # OUTPUT: «(bacon eggs bacon)␤» 
 
my $random_dishes := $breakfast.roll(*);
say $random_dishes[^5];                               # OUTPUT: «(bacon eggs bacon bacon bacon)␤»

method pairs

method pairs(Baggy:D: --> Seq:D)

Returns all elements and their respective weights as a Seq of Pairs where the key is the element itself and the value is the weight of that element.

my $breakfast = bag <bacon eggs bacon>;
my $seq = $breakfast.pairs;
say $seq.sort;                                    # OUTPUT: «(bacon => 2 eggs => 1)␤»

method antipairs

method antipairs(Baggy:D: --> Seq:D)

Returns all elements and their respective weights as a Seq of Pair objects, where the element itself is the value and the weight of that element is the key, i.e. the opposite of method pairs.

my $breakfast = bag <bacon eggs bacon>;
my $seq = $breakfast.antipairs;
say $seq.sort;                                    # OUTPUT: «(1 => eggs 2 => bacon)␤»

method invert

method invert(Baggy:D: --> Seq:D)

Returns all elements and their respective weights as a Seq of Pair objects, where the element itself is the value and the weight of that element is the key, i.e. the opposite of method pairs. Except for some esoteric cases, invert on a Baggy type returns the same result as antipairs.

my $breakfast = bag <bacon eggs bacon>;
my $seq = $breakfast.invert;
say $seq.sort;                                    # OUTPUT: «(1 => eggs 2 => bacon)␤»

method classify-list

multi method classify-list(&mapper, *@list --> Baggy:D)
multi method classify-list(%mapper, *@list --> Baggy:D)
multi method classify-list(@mapper, *@list --> Baggy:D)

Populates a mutable Baggy by classifying the possibly-empty @list of values using the given mapper. The @list cannot be lazy.

say BagHash.new.classify-list: { $_ %% 2 ?? 'even' !! 'odd' }, ^10;
# OUTPUT: BagHash(even(5) odd(5)) 
 
my @mapper = <zero one two three four five>;
say MixHash.new.classify-list: @mapper, 1, 2, 3, 4, 4, 6;
# OUTPUT: MixHash((Any) two three four(2) one)

The mapper can be a Callable that takes a single argument, an Associative, or an Iterable. With Associative and an Iterable mappers, the values in the @list represent the key and index of the mapper's value respectively. A Callable mapper will be executed once per each item in the @list, with that item as the argument and its return value will be used as the mapper's value.

The mapper's value is used as the key of the Baggy that will be incremented by 1. See .categorize-list if you wish to classify an item into multiple categories at once.

Note: unlike the Hash's .classify-list, returning an Iterable mapper's value will throw, as Baggy types do not support nested classification. For the same reason, Baggy's .classify-list does not accept :&as parameter.

method categorize-list

multi method categorize-list(&mapper, *@list --> Baggy:D)
multi method categorize-list(%mapper, *@list --> Baggy:D)
multi method categorize-list(@mapper, *@list --> Baggy:D)

Populates a mutable Baggy by categorizing the possibly-empty @list of values using the given mapper. The @list cannot be lazy.

say BagHash.new.categorize-list: {
    gather {
        take 'largish' if $_ > 5;
        take .is-prime ?? 'prime' !! 'non-prime';
        take $_ %% 2   ?? 'even'  !! 'odd';
    }
}, ^10;
# OUTPUT: BagHash(largish(4) even(5) non-prime(6) prime(4) odd(5)) 
 
my %mapper = :sugar<sweet white>, :lemon<sour>, :cake('sweet', 'is-a-lie');
say MixHash.new.categorize-list: %mapper, <sugar lemon cake>;
# OUTPUT: MixHash(is-a-lie sour white sweet(2))

The mapper can be a Callable that takes a single argument, an Associative, or an Iterable. With Associative and an Iterable mappers, the values in the @list represent the key and index of the mapper's value respectively. A Callable mapper will be executed once per each item in the @list, with that item as the argument and its return value will be used as the mapper's value.

The mapper's value is used as a possibly-empty list of keys of the Baggy that will be incremented by 1.

Note: unlike the Hash's .categorize-list, returning a list of Iterable as mapper's value will throw, as Baggy types do not support nested categorization. For the same reason, Baggy's .categorize-list does not accept :&as parameter.

method keys

method keys(Baggy:D: --> Seq:D)

Returns a Seq of all keys in the Baggy object without taking their individual weights into account as opposed to kxxv.

my $breakfast = bag <eggs spam spam spam>;
say $breakfast.keys.sort;                        # OUTPUT: «(eggs spam)␤» 
 
my $n = ("a" => 5, "b" => 2).BagHash;
say $n.keys.sort;                                # OUTPUT: «(a b)␤»

method values

method values(Baggy:D: --> Seq:D)

Returns a Seq of all values, i.e. weights, in the Baggy object.

my $breakfast = bag <eggs spam spam spam>;
say $breakfast.values.sort;                      # OUTPUT: «(1 3)␤» 
 
my $n = ("a" => 5, "b" => 2, "a" => 1).BagHash;
say $n.values.sort;                              # OUTPUT: «(2 6)␤»

method kv

method kv(Baggy:D: --> Seq:D)

Returns a Seq of keys and values interleaved.

my $breakfast = bag <eggs spam spam spam>;
say $breakfast.kv;                                # OUTPUT: «(spam 3 eggs 1)␤» 
 
my $n = ("a" => 5, "b" => 2, "a" => 1).BagHash;
say $n.kv;                                        # OUTPUT: «(a 6 b 2)␤»

method kxxv

method kxxv(Baggy:D: --> Seq:D)

Returns a Seq of the keys of the invocant, with each key multiplied by its weight. Note that kxxv only works for Baggy types which have integer weights, i.e. Bag and BagHash.

my $breakfast = bag <spam eggs spam spam bacon>;
say $breakfast.kxxv.sort;                         # OUTPUT: «(bacon eggs spam spam spam)␤» 
 
my $n = ("a" => 0, "b" => 1, "b" => 2).BagHash;
say $n.kxxv;                                      # OUTPUT: «(b b b)␤»

method elems

method elems(Baggy:D: --> Int:D)

Returns the number of elements in the Baggy object without taking the individual elements' weight into account.

my $breakfast = bag <eggs spam spam spam>;
say $breakfast.elems;                             # OUTPUT: «2␤» 
 
my $n = ("b" => 9.4, "b" => 2).MixHash;
say $n.elems;                                     # OUTPUT: «1␤»

method total

method total(Baggy:D:)

Returns the sum of weights for all elements in the Baggy object.

my $breakfast = bag <eggs spam spam bacon>;
say $breakfast.total;                             # OUTPUT: «4␤» 
 
my $n = ("a" => 5, "b" => 1, "b" => 2).BagHash;
say $n.total;                                     # OUTPUT: «8␤»

method default

method default(Baggy:D: --> 0)

Returns zero.

my $breakfast = bag <eggs bacon>;
say $breakfast.default;                           # OUTPUT: «0␤»

method hash

method hash(Baggy:D: --> Hash:D)

Returns a Hash where the elements of the invocant are the keys and their respective weights the values.

my $breakfast = bag <eggs bacon bacon>;
my $h = $breakfast.hash;
say $h.^name;                    # OUTPUT: «Hash[Any,Any]␤» 
say $h;                          # OUTPUT: «{bacon => 2, eggs => 1}␤»

method Bool

method Bool(Baggy:D: --> Bool:D)

Returns True if the invocant contains at least one element.

my $breakfast = ('eggs' => 1).BagHash;
say $breakfast.Bool;                              # OUTPUT: «True␤» 
                                                  # (since we have one element) 
$breakfast<eggs> = 0;                             # weight == 0 will lead to element removal 
say $breakfast.Bool;                              # OUTPUT: «False␤»

method Set

method Set(--> Set:D)

Returns a Set whose elements are the keys of the invocant.

my $breakfast = (eggs => 2, bacon => 3).BagHash;
say $breakfast.Set;                               # OUTPUT: «Set(bacon eggs)␤»

method SetHash

method SetHash(--> SetHash:D)

Returns a SetHash whose elements are the keys of the invocant.

my $breakfast = (eggs => 2, bacon => 3).BagHash;
my $sh = $breakfast.SetHash;
say $sh.^name;                            # OUTPUT: «SetHash␤» 
say $sh.elems;                            # OUTPUT: «2␤»

method ACCEPTS

method ACCEPTS($other --> Bool:D)

Used in smartmatching if the right-hand side is a Baggy.

If the right-hand side is the type object, i.e. Baggy, the method returns True if $other does Baggy otherwise False is returned.

If the right-hand side is a Baggy object, True is returned only if $other has the same elements, with the same weights, as the invocant.

my $breakfast = bag <eggs bacon>;
say $breakfast ~~ Baggy;                            # OUTPUT: «True␤» 
say $breakfast.does(Baggy);                         # OUTPUT: «True␤» 
 
my $second-breakfast = (eggs => 1, bacon => 1).Mix;
say $breakfast ~~ $second-breakfast;                # OUTPUT: «True␤» 
 
my $third-breakfast = (eggs => 1, bacon => 2).Bag;
say $second-breakfast ~~ $third-breakfast;          # OUTPUT: «False␤»

See Also

Sets, Bags, and Mixes