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#![cfg(feature = "use_std")]
use std::collections::HashMap;
use std::hash::Hash;
use std::iter::Iterator;
/// Return a `HashMap` of keys mapped to a list of their corresponding values.
///
/// See [`.into_group_map()`](../trait.Itertools.html#method.into_group_map)
/// for more information.
pub fn into_group_map<I, K, V>(iter: I) -> HashMap<K, Vec<V>>
where I: Iterator<Item=(K, V)>,
K: Hash + Eq,
{
let mut lookup = HashMap::new();
iter.for_each(|(key, val)| {
lookup.entry(key).or_insert_with(Vec::new).push(val);
});
lookup
}
pub fn into_group_map_by<I, K, V>(iter: I, f: impl Fn(&V) -> K) -> HashMap<K, Vec<V>>
where
I: Iterator<Item=V>,
K: Hash + Eq,
{
into_group_map(
iter.map(|v| (f(&v), v))
)
}
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