Source code
Revision control
Copy as Markdown
Other Tools
#![cfg(feature = "use_std")]
use crate::MinMaxResult;
use std::collections::HashMap;
use std::cmp::Ordering;
use std::hash::Hash;
use std::iter::Iterator;
use std::ops::{Add, Mul};
/// A wrapper to allow for an easy [`into_grouping_map_by`](crate::Itertools::into_grouping_map_by)
#[derive(Clone, Debug)]
pub struct MapForGrouping<I, F>(I, F);
impl<I, F> MapForGrouping<I, F> {
pub(crate) fn new(iter: I, key_mapper: F) -> Self {
Self(iter, key_mapper)
}
}
impl<K, V, I, F> Iterator for MapForGrouping<I, F>
where I: Iterator<Item = V>,
K: Hash + Eq,
F: FnMut(&V) -> K,
{
type Item = (K, V);
fn next(&mut self) -> Option<Self::Item> {
self.0.next().map(|val| ((self.1)(&val), val))
}
}
/// Creates a new `GroupingMap` from `iter`
pub fn new<I, K, V>(iter: I) -> GroupingMap<I>
where I: Iterator<Item = (K, V)>,
K: Hash + Eq,
{
GroupingMap { iter }
}
/// `GroupingMapBy` is an intermediate struct for efficient group-and-fold operations.
///
/// See [`GroupingMap`] for more informations.
pub type GroupingMapBy<I, F> = GroupingMap<MapForGrouping<I, F>>;
/// `GroupingMap` is an intermediate struct for efficient group-and-fold operations.
/// It groups elements by their key and at the same time fold each group
/// using some aggregating operation.
///
/// No method on this struct performs temporary allocations.
#[derive(Clone, Debug)]
#[must_use = "GroupingMap is lazy and do nothing unless consumed"]
pub struct GroupingMap<I> {
iter: I,
}
impl<I, K, V> GroupingMap<I>
where I: Iterator<Item = (K, V)>,
K: Hash + Eq,
{
/// This is the generic way to perform any operation on a `GroupingMap`.
/// It's suggested to use this method only to implement custom operations
/// when the already provided ones are not enough.
///
/// Groups elements from the `GroupingMap` source by key and applies `operation` to the elements
/// of each group sequentially, passing the previously accumulated value, a reference to the key
/// and the current element as arguments, and stores the results in an `HashMap`.
///
/// The `operation` function is invoked on each element with the following parameters:
/// - the current value of the accumulator of the group if there is currently one;
/// - a reference to the key of the group this element belongs to;
/// - the element from the source being aggregated;
///
/// If `operation` returns `Some(element)` then the accumulator is updated with `element`,
/// otherwise the previous accumulation is discarded.
///
/// Return a `HashMap` associating the key of each group with the result of aggregation of
/// that group's elements. If the aggregation of the last element of a group discards the
/// accumulator then there won't be an entry associated to that group's key.
///
/// ```
/// use itertools::Itertools;
///
/// let data = vec![2, 8, 5, 7, 9, 0, 4, 10];
/// let lookup = data.into_iter()
/// .into_grouping_map_by(|&n| n % 4)
/// .aggregate(|acc, _key, val| {
/// if val == 0 || val == 10 {
/// None
/// } else {
/// Some(acc.unwrap_or(0) + val)
/// }
/// });
///
/// assert_eq!(lookup[&0], 4); // 0 resets the accumulator so only 4 is summed
/// assert_eq!(lookup[&1], 5 + 9);
/// assert_eq!(lookup.get(&2), None); // 10 resets the accumulator and nothing is summed afterward
/// assert_eq!(lookup[&3], 7);
/// assert_eq!(lookup.len(), 3); // The final keys are only 0, 1 and 2
/// ```
pub fn aggregate<FO, R>(self, mut operation: FO) -> HashMap<K, R>
where FO: FnMut(Option<R>, &K, V) -> Option<R>,
{
let mut destination_map = HashMap::new();
self.iter.for_each(|(key, val)| {
let acc = destination_map.remove(&key);
if let Some(op_res) = operation(acc, &key, val) {
destination_map.insert(key, op_res);
}
});
destination_map
}
/// Groups elements from the `GroupingMap` source by key and applies `operation` to the elements
/// of each group sequentially, passing the previously accumulated value, a reference to the key
/// and the current element as arguments, and stores the results in a new map.
///
/// `init` is the value from which will be cloned the initial value of each accumulator.
///
/// `operation` is a function that is invoked on each element with the following parameters:
/// - the current value of the accumulator of the group;
/// - a reference to the key of the group this element belongs to;
/// - the element from the source being accumulated.
///
/// Return a `HashMap` associating the key of each group with the result of folding that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = (1..=7)
/// .into_grouping_map_by(|&n| n % 3)
/// .fold(0, |acc, _key, val| acc + val);
///
/// assert_eq!(lookup[&0], 3 + 6);
/// assert_eq!(lookup[&1], 1 + 4 + 7);
/// assert_eq!(lookup[&2], 2 + 5);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn fold<FO, R>(self, init: R, mut operation: FO) -> HashMap<K, R>
where R: Clone,
FO: FnMut(R, &K, V) -> R,
{
self.aggregate(|acc, key, val| {
let acc = acc.unwrap_or_else(|| init.clone());
Some(operation(acc, key, val))
})
}
/// Groups elements from the `GroupingMap` source by key and applies `operation` to the elements
/// of each group sequentially, passing the previously accumulated value, a reference to the key
/// and the current element as arguments, and stores the results in a new map.
///
/// This is similar to [`fold`] but the initial value of the accumulator is the first element of the group.
///
/// `operation` is a function that is invoked on each element with the following parameters:
/// - the current value of the accumulator of the group;
/// - a reference to the key of the group this element belongs to;
/// - the element from the source being accumulated.
///
/// Return a `HashMap` associating the key of each group with the result of folding that group's elements.
///
/// [`fold`]: GroupingMap::fold
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = (1..=7)
/// .into_grouping_map_by(|&n| n % 3)
/// .fold_first(|acc, _key, val| acc + val);
///
/// assert_eq!(lookup[&0], 3 + 6);
/// assert_eq!(lookup[&1], 1 + 4 + 7);
/// assert_eq!(lookup[&2], 2 + 5);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn fold_first<FO>(self, mut operation: FO) -> HashMap<K, V>
where FO: FnMut(V, &K, V) -> V,
{
self.aggregate(|acc, key, val| {
Some(match acc {
Some(acc) => operation(acc, key, val),
None => val,
})
})
}
/// Groups elements from the `GroupingMap` source by key and collects the elements of each group in
/// an instance of `C`. The iteration order is preserved when inserting elements.
///
/// Return a `HashMap` associating the key of each group with the collection containing that group's elements.
///
/// ```
/// use itertools::Itertools;
/// use std::collections::HashSet;
///
/// let lookup = vec![0, 1, 2, 3, 4, 5, 6, 2, 3, 6].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .collect::<HashSet<_>>();
///
/// assert_eq!(lookup[&0], vec![0, 3, 6].into_iter().collect::<HashSet<_>>());
/// assert_eq!(lookup[&1], vec![1, 4].into_iter().collect::<HashSet<_>>());
/// assert_eq!(lookup[&2], vec![2, 5].into_iter().collect::<HashSet<_>>());
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn collect<C>(self) -> HashMap<K, C>
where C: Default + Extend<V>,
{
let mut destination_map = HashMap::new();
self.iter.for_each(|(key, val)| {
destination_map.entry(key).or_insert_with(C::default).extend(Some(val));
});
destination_map
}
/// Groups elements from the `GroupingMap` source by key and finds the maximum of each group.
///
/// If several elements are equally maximum, the last element is picked.
///
/// Returns a `HashMap` associating the key of each group with the maximum of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .max();
///
/// assert_eq!(lookup[&0], 12);
/// assert_eq!(lookup[&1], 7);
/// assert_eq!(lookup[&2], 8);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn max(self) -> HashMap<K, V>
where V: Ord,
{
self.max_by(|_, v1, v2| V::cmp(v1, v2))
}
/// Groups elements from the `GroupingMap` source by key and finds the maximum of each group
/// with respect to the specified comparison function.
///
/// If several elements are equally maximum, the last element is picked.
///
/// Returns a `HashMap` associating the key of each group with the maximum of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .max_by(|_key, x, y| y.cmp(x));
///
/// assert_eq!(lookup[&0], 3);
/// assert_eq!(lookup[&1], 1);
/// assert_eq!(lookup[&2], 5);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn max_by<F>(self, mut compare: F) -> HashMap<K, V>
where F: FnMut(&K, &V, &V) -> Ordering,
{
self.fold_first(|acc, key, val| match compare(key, &acc, &val) {
Ordering::Less | Ordering::Equal => val,
Ordering::Greater => acc
})
}
/// Groups elements from the `GroupingMap` source by key and finds the element of each group
/// that gives the maximum from the specified function.
///
/// If several elements are equally maximum, the last element is picked.
///
/// Returns a `HashMap` associating the key of each group with the maximum of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .max_by_key(|_key, &val| val % 4);
///
/// assert_eq!(lookup[&0], 3);
/// assert_eq!(lookup[&1], 7);
/// assert_eq!(lookup[&2], 5);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn max_by_key<F, CK>(self, mut f: F) -> HashMap<K, V>
where F: FnMut(&K, &V) -> CK,
CK: Ord,
{
self.max_by(|key, v1, v2| f(key, v1).cmp(&f(key, v2)))
}
/// Groups elements from the `GroupingMap` source by key and finds the minimum of each group.
///
/// If several elements are equally minimum, the first element is picked.
///
/// Returns a `HashMap` associating the key of each group with the minimum of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .min();
///
/// assert_eq!(lookup[&0], 3);
/// assert_eq!(lookup[&1], 1);
/// assert_eq!(lookup[&2], 5);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn min(self) -> HashMap<K, V>
where V: Ord,
{
self.min_by(|_, v1, v2| V::cmp(v1, v2))
}
/// Groups elements from the `GroupingMap` source by key and finds the minimum of each group
/// with respect to the specified comparison function.
///
/// If several elements are equally minimum, the first element is picked.
///
/// Returns a `HashMap` associating the key of each group with the minimum of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .min_by(|_key, x, y| y.cmp(x));
///
/// assert_eq!(lookup[&0], 12);
/// assert_eq!(lookup[&1], 7);
/// assert_eq!(lookup[&2], 8);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn min_by<F>(self, mut compare: F) -> HashMap<K, V>
where F: FnMut(&K, &V, &V) -> Ordering,
{
self.fold_first(|acc, key, val| match compare(key, &acc, &val) {
Ordering::Less | Ordering::Equal => acc,
Ordering::Greater => val
})
}
/// Groups elements from the `GroupingMap` source by key and finds the element of each group
/// that gives the minimum from the specified function.
///
/// If several elements are equally minimum, the first element is picked.
///
/// Returns a `HashMap` associating the key of each group with the minimum of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .min_by_key(|_key, &val| val % 4);
///
/// assert_eq!(lookup[&0], 12);
/// assert_eq!(lookup[&1], 4);
/// assert_eq!(lookup[&2], 8);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn min_by_key<F, CK>(self, mut f: F) -> HashMap<K, V>
where F: FnMut(&K, &V) -> CK,
CK: Ord,
{
self.min_by(|key, v1, v2| f(key, v1).cmp(&f(key, v2)))
}
/// Groups elements from the `GroupingMap` source by key and find the maximum and minimum of
/// each group.
///
/// If several elements are equally maximum, the last element is picked.
/// If several elements are equally minimum, the first element is picked.
///
/// See [.minmax()](crate::Itertools::minmax) for the non-grouping version.
///
/// Differences from the non grouping version:
/// - It never produces a `MinMaxResult::NoElements`
/// - It doesn't have any speedup
///
/// Returns a `HashMap` associating the key of each group with the minimum and maximum of that group's elements.
///
/// ```
/// use itertools::Itertools;
/// use itertools::MinMaxResult::{OneElement, MinMax};
///
/// let lookup = vec![1, 3, 4, 5, 7, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .minmax();
///
/// assert_eq!(lookup[&0], MinMax(3, 12));
/// assert_eq!(lookup[&1], MinMax(1, 7));
/// assert_eq!(lookup[&2], OneElement(5));
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn minmax(self) -> HashMap<K, MinMaxResult<V>>
where V: Ord,
{
self.minmax_by(|_, v1, v2| V::cmp(v1, v2))
}
/// Groups elements from the `GroupingMap` source by key and find the maximum and minimum of
/// each group with respect to the specified comparison function.
///
/// If several elements are equally maximum, the last element is picked.
/// If several elements are equally minimum, the first element is picked.
///
/// It has the same differences from the non-grouping version as `minmax`.
///
/// Returns a `HashMap` associating the key of each group with the minimum and maximum of that group's elements.
///
/// ```
/// use itertools::Itertools;
/// use itertools::MinMaxResult::{OneElement, MinMax};
///
/// let lookup = vec![1, 3, 4, 5, 7, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .minmax_by(|_key, x, y| y.cmp(x));
///
/// assert_eq!(lookup[&0], MinMax(12, 3));
/// assert_eq!(lookup[&1], MinMax(7, 1));
/// assert_eq!(lookup[&2], OneElement(5));
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn minmax_by<F>(self, mut compare: F) -> HashMap<K, MinMaxResult<V>>
where F: FnMut(&K, &V, &V) -> Ordering,
{
self.aggregate(|acc, key, val| {
Some(match acc {
Some(MinMaxResult::OneElement(e)) => {
if compare(key, &val, &e) == Ordering::Less {
MinMaxResult::MinMax(val, e)
} else {
MinMaxResult::MinMax(e, val)
}
}
Some(MinMaxResult::MinMax(min, max)) => {
if compare(key, &val, &min) == Ordering::Less {
MinMaxResult::MinMax(val, max)
} else if compare(key, &val, &max) != Ordering::Less {
MinMaxResult::MinMax(min, val)
} else {
MinMaxResult::MinMax(min, max)
}
}
None => MinMaxResult::OneElement(val),
Some(MinMaxResult::NoElements) => unreachable!(),
})
})
}
/// Groups elements from the `GroupingMap` source by key and find the elements of each group
/// that gives the minimum and maximum from the specified function.
///
/// If several elements are equally maximum, the last element is picked.
/// If several elements are equally minimum, the first element is picked.
///
/// It has the same differences from the non-grouping version as `minmax`.
///
/// Returns a `HashMap` associating the key of each group with the minimum and maximum of that group's elements.
///
/// ```
/// use itertools::Itertools;
/// use itertools::MinMaxResult::{OneElement, MinMax};
///
/// let lookup = vec![1, 3, 4, 5, 7, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .minmax_by_key(|_key, &val| val % 4);
///
/// assert_eq!(lookup[&0], MinMax(12, 3));
/// assert_eq!(lookup[&1], MinMax(4, 7));
/// assert_eq!(lookup[&2], OneElement(5));
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn minmax_by_key<F, CK>(self, mut f: F) -> HashMap<K, MinMaxResult<V>>
where F: FnMut(&K, &V) -> CK,
CK: Ord,
{
self.minmax_by(|key, v1, v2| f(key, v1).cmp(&f(key, v2)))
}
/// Groups elements from the `GroupingMap` source by key and sums them.
///
/// This is just a shorthand for `self.fold_first(|acc, _, val| acc + val)`.
/// It is more limited than `Iterator::sum` since it doesn't use the `Sum` trait.
///
/// Returns a `HashMap` associating the key of each group with the sum of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .sum();
///
/// assert_eq!(lookup[&0], 3 + 9 + 12);
/// assert_eq!(lookup[&1], 1 + 4 + 7);
/// assert_eq!(lookup[&2], 5 + 8);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn sum(self) -> HashMap<K, V>
where V: Add<V, Output = V>
{
self.fold_first(|acc, _, val| acc + val)
}
/// Groups elements from the `GroupingMap` source by key and multiply them.
///
/// This is just a shorthand for `self.fold_first(|acc, _, val| acc * val)`.
/// It is more limited than `Iterator::product` since it doesn't use the `Product` trait.
///
/// Returns a `HashMap` associating the key of each group with the product of that group's elements.
///
/// ```
/// use itertools::Itertools;
///
/// let lookup = vec![1, 3, 4, 5, 7, 8, 9, 12].into_iter()
/// .into_grouping_map_by(|&n| n % 3)
/// .product();
///
/// assert_eq!(lookup[&0], 3 * 9 * 12);
/// assert_eq!(lookup[&1], 1 * 4 * 7);
/// assert_eq!(lookup[&2], 5 * 8);
/// assert_eq!(lookup.len(), 3);
/// ```
pub fn product(self) -> HashMap<K, V>
where V: Mul<V, Output = V>,
{
self.fold_first(|acc, _, val| acc * val)
}
}