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Mojo struct

Counter

struct Counter[V: KeyElement]

A container for counting hashable items.

The value type must be specified statically, unlike a Python Counter, which can accept arbitrary value types.

The value type must implement the KeyElement trait, as its values are stored in the dictionary as keys.

Usage:

from collections import Counter
var c = Counter[String](List("a", "a", "a", "b", "b", "c", "d", "c", "c"))
print(c["a"]) # prints 3
print(c["b"]) # prints 2
from collections import Counter
var c = Counter[String](List("a", "a", "a", "b", "b", "c", "d", "c", "c"))
print(c["a"]) # prints 3
print(c["b"]) # prints 2

Parameters​

  • ​V (KeyElement): The value type to be counted. Currently must be KeyElement.

Implemented traits​

AnyType, Boolable, CollectionElement, Copyable, Movable, Sized, UnknownDestructibility

Methods​

__init__​

__init__(out self)

Create a new, empty Counter object.

@implicit __init__(out self, items: List[V, hint_trivial_type])

Create a from an input iterable.

Args:

  • ​items (List[V, hint_trivial_type]): A list of items to count.

__init__(out self, *, other: Self)

Create a new Counter by copying another Counter.

Args:

  • ​other (Self): The Counter to copy.

__bool__​

__bool__(self) -> Bool

Check if the Counter is empty or not.

Returns:

False if the Counter is empty, True otherwise.

__getitem__​

__getitem__(self, key: V) -> Int

Get the count of a key.

Args:

  • ​key (V): The key to get the count of.

Returns:

The count of the key.

__setitem__​

__setitem__(mut self, value: V, count: Int)

Set a value in the keyword Counter by key.

Args:

  • ​value (V): The value to associate with the specified count.
  • ​count (Int): The count to store in the Counter.

__neg__​

__neg__(self) -> Self

Substract from an empty Counter. Strips positive and zero counts, and flips the sign on negative counts.

Returns:

A new Counter with stripped counts and negative counts.

__pos__​

__pos__(self) -> Self

Return a shallow copy of the Counter, stripping non-positive counts.

Returns:

A shallow copy of the Counter.

__lt__​

__lt__(self, other: Self) -> Bool

Check if all counts are less than in the other Counter.

Args:

  • ​other (Self): The other Counter to compare to.

Returns:

True if all counts are less than in the other Counter, False otherwise.

__le__​

__le__(self, other: Self) -> Bool

Check if all counts are less than or equal to the other Counter.

Args:

  • ​other (Self): The other Counter to compare to.

Returns:

True if all counts are less than or equal to the other Counter, False otherwise.

__eq__​

__eq__(self, other: Self) -> Bool

Check if all counts agree. Missing counts are treated as zero.

Args:

  • ​other (Self): The other Counter to compare to.

Returns:

True if the two Counters are equal, False otherwise.

__ne__​

__ne__(self, other: Self) -> Bool

Check if all counts disagree. Missing counts are treated as zero.

Args:

  • ​other (Self): The other Counter to compare to.

Returns:

True if the two Counters are not equal, False otherwise.

__gt__​

__gt__(self, other: Self) -> Bool

Check if all counts are greater than in the other Counter.

Args:

  • ​other (Self): The other Counter to compare to.

Returns:

True if all counts are greater than in the other Counter, False otherwise.

__ge__​

__ge__(self, other: Self) -> Bool

Check if all counts are greater than or equal to the other Counter.

Args:

  • ​other (Self): The other Counter to compare to.

Returns:

True if all counts are greater than or equal to the other Counter, False otherwise.

__contains__​

__contains__(self, key: V) -> Bool

Check if a given key is in the dictionary or not.

Args:

  • ​key (V): The key to check.

Returns:

True if there key exists in the dictionary, False otherwise.

__add__​

__add__(self, other: Self) -> Self

Add counts from two Counters.

Args:

  • ​other (Self): The other Counter to add to this Counter.

Returns:

A new Counter with the counts from both Counters added together.

__sub__​

__sub__(self, other: Self) -> Self

Subtract counts, but keep only results with positive counts.

Args:

  • ​other (Self): The other Counter to subtract from this Counter.

Returns:

A new Counter with the counts from the other Counter subtracted from this Counter.

__and__​

__and__(self, other: Self) -> Self

Intersection: keep common elements with the minimum count.

Args:

  • ​other (Self): The other Counter to intersect with.

Returns:

A new Counter with the common elements and the minimum count of the two Counters.

__or__​

__or__(self, other: Self) -> Self

Union: keep all elements with the maximum count.

Args:

  • ​other (Self): The other Counter to union with.

Returns:

A new Counter with all elements and the maximum count of the two Counters.

__iadd__​

__iadd__(mut self, other: Self)

Add counts from another Counter to this Counter.

Args:

  • ​other (Self): The other Counter to add to this Counter.

__isub__​

__isub__(mut self, other: Self)

Subtract counts from another Counter from this Counter.

Args:

  • ​other (Self): The other Counter to subtract from this Counter.

__iand__​

__iand__(mut self, other: Self)

Intersection: keep common elements with the minimum count.

Args:

  • ​other (Self): The other Counter to intersect with.

__ior__​

__ior__(mut self, other: Self)

Union: keep all elements with the maximum count.

Args:

  • ​other (Self): The other Counter to union with.

fromkeys​

static fromkeys(keys: List[V, hint_trivial_type], value: Int) -> Self

Create a new Counter from a list of keys and a default value.

Args:

  • ​keys (List[V, hint_trivial_type]): The keys to create the Counter from.
  • ​value (Int): The default value to associate with each key.

Returns:

A new Counter with the keys and default value.

__iter__​

__iter__(self) -> _DictKeyIter[V, Int, self._data]

Iterate over the keyword dict's keys as immutable references.

Returns:

An iterator of immutable references to the Counter values.

__len__​

__len__(self) -> Int

Returns the number of elements currently stored in the Counter.

Returns:

The number of elements in the Counter.

get​

get(self, value: V) -> Optional[Int]

Get a value from the counter.

Args:

  • ​value (V): The value to search for in the Counter.

Returns:

An optional value containing a copy of the value if it was present, otherwise an empty Optional.

get(self, value: V, default: Int) -> Int

Get a value from the Counter.

Args:

  • ​value (V): The value to search for in the counter.
  • ​default (Int): Default count to return.

Returns:

A copy of the value if it was present, otherwise default.

pop​

pop(mut self, value: V) -> Int

Remove a value from the Counter by value.

Args:

  • ​value (V): The value to remove from the Counter.

Returns:

The value associated with the key, if it was in the Counter.

Raises:

"KeyError" if the key was not present in the Counter.

pop(mut self, value: V, owned default: Int) -> Int

Remove a value from the Counter by value.

Args:

  • ​value (V): The value to remove from the Counter.
  • ​default (Int): Optionally provide a default value to return if the value was not found instead of raising.

Returns:

The value associated with the key, if it was in the Counter. If it wasn't, return the provided default value instead.

Raises:

"KeyError" if the key was not present in the Counter and no default value was provided.

keys​

keys(ref self) -> _DictKeyIter[V, Int, self_is_origin._data]

Iterate over the Counter's keys as immutable references.

Returns:

An iterator of immutable references to the Counter keys.

values​

values(ref self) -> _DictValueIter[V, Int, self_is_origin._data]

Iterate over the Counter's values as references.

Returns:

An iterator of references to the Counter values.

items​

items(self) -> _DictEntryIter[V, Int, self._data]

Iterate over the dict's entries as immutable references.

Returns:

An iterator of immutable references to the Counter entries.

clear​

clear(mut self)

Remove all elements from the Counter.

popitem​

popitem(mut self) -> CountTuple[V]

Remove and return an arbitrary (key, value) pair from the Counter.

Returns:

A CountTuple containing the key and value of the removed item.

Raises:

"KeyError" if the Counter is empty.

total​

total(self) -> Int

Return the total of all counts in the Counter.

Returns:

The total of all counts in the Counter.

most_common​

most_common(self, n: Int) -> List[CountTuple[V]]

Return a list of the n most common elements and their counts from the most common to the least.

Args:

  • ​n (Int): The number of most common elements to return.

Returns:

A list of the n most common elements and their counts.

elements​

elements(self) -> List[V]

Return an iterator over elements repeating each as many times as its count.

Returns:

An iterator over the elements in the Counter.

update​

update(mut self, other: Self)

Update the Counter, like dict.update() but add counts instead of replacing them.

Args:

  • ​other (Self): The Counter to update this Counter with.

subtract​

subtract(mut self, other: Self)

Subtract count. Both inputs and outputs may be zero or negative.

Args:

  • ​other (Self): The Counter to subtract from this Counter.