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1. fromList :: (Eq k, Hashable k) => [(k, v)] -> HashMap k v

   unordered-containers	Data.HashMap.Lazy

   Construct a map with the supplied mappings. If the list contains duplicate mappings, the later mappings take precedence.

2. fromListWith :: (Eq k, Hashable k) => (v -> v -> v) -> [(k, v)] -> HashMap k v

   unordered-containers	Data.HashMap.Lazy

   Construct a map from a list of elements. Uses the provided function f to merge duplicate entries with (f newVal oldVal).

   Examples

   Given a list xs, create a map with the number of occurrences of each element in xs:

   let xs = ['a', 'b', 'a']
   in fromListWith (+) [ (x, 1) | x <- xs ]
   
   = fromList [('a', 2), ('b', 1)]
   

   Given a list of key-value pairs xs :: [(k, v)], group all values by their keys and return a HashMap k [v].

   let xs = [('a', 1), ('b', 2), ('a', 3)]
   in fromListWith (++) [ (k, [v]) | (k, v) <- xs ]
   
   = fromList [('a', [3, 1]), ('b', [2])]
   

   Note that the lists in the resulting map contain elements in reverse order from their occurrences in the original list. More generally, duplicate entries are accumulated as follows; this matters when f is not commutative or not associative.

   fromListWith f [(k, a), (k, b), (k, c), (k, d)]
   = fromList [(k, f d (f c (f b a)))]
   

3. fromListWithKey :: (Eq k, Hashable k) => (k -> v -> v -> v) -> [(k, v)] -> HashMap k v

   unordered-containers	Data.HashMap.Lazy

   Construct a map from a list of elements. Uses the provided function to merge duplicate entries.

   Examples

   Given a list of key-value pairs where the keys are of different flavours, e.g:

   data Key = Div | Sub
   

   and the values need to be combined differently when there are duplicates, depending on the key:

   combine Div = div
   combine Sub = (-)
   

   then fromListWithKey can be used as follows:

   fromListWithKey combine [(Div, 2), (Div, 6), (Sub, 2), (Sub, 3)]
   = fromList [(Div, 3), (Sub, 1)]
   

   More generally, duplicate entries are accumulated as follows;

   fromListWith f [(k, a), (k, b), (k, c), (k, d)]
   = fromList [(k, f k d (f k c (f k b a)))]
   

4. toList :: HashMap k v -> [(k, v)]

   unordered-containers	Data.HashMap.Lazy

   Return a list of this map's elements. The list is produced lazily. The order of its elements is unspecified.

5. fromList :: (Eq k, Hashable k) => [(k, v)] -> HashMap k v

   unordered-containers	Data.HashMap.Strict

   Construct a map with the supplied mappings. If the list contains duplicate mappings, the later mappings take precedence.

6. fromListWith :: (Eq k, Hashable k) => (v -> v -> v) -> [(k, v)] -> HashMap k v

   unordered-containers	Data.HashMap.Strict

   Construct a map from a list of elements. Uses the provided function f to merge duplicate entries with (f newVal oldVal).

   Examples

   Given a list xs, create a map with the number of occurrences of each element in xs:

   let xs = ['a', 'b', 'a']
   in fromListWith (+) [ (x, 1) | x <- xs ]
   
   = fromList [('a', 2), ('b', 1)]
   

   Given a list of key-value pairs xs :: [(k, v)], group all values by their keys and return a HashMap k [v].

   let xs = ('a', 1), ('b', 2), ('a', 3)]
   in fromListWith (++) [ (k, [v]) | (k, v) <- xs ]
   
   = fromList [('a', [3, 1]), ('b', [2])]
   

   Note that the lists in the resulting map contain elements in reverse order from their occurrences in the original list. More generally, duplicate entries are accumulated as follows; this matters when f is not commutative or not associative.

   fromListWith f [(k, a), (k, b), (k, c), (k, d)]
   = fromList [(k, f d (f c (f b a)))]
   

7. fromListWithKey :: (Eq k, Hashable k) => (k -> v -> v -> v) -> [(k, v)] -> HashMap k v

   unordered-containers	Data.HashMap.Strict

   Construct a map from a list of elements. Uses the provided function to merge duplicate entries.

   Examples

   Given a list of key-value pairs where the keys are of different flavours, e.g:

   data Key = Div | Sub
   

   and the values need to be combined differently when there are duplicates, depending on the key:

   combine Div = div
   combine Sub = (-)
   

   then fromListWithKey can be used as follows:

   fromListWithKey combine [(Div, 2), (Div, 6), (Sub, 2), (Sub, 3)]
   = fromList [(Div, 3), (Sub, 1)]
   

   More generally, duplicate entries are accumulated as follows;

   fromListWith f [(k, a), (k, b), (k, c), (k, d)]
   = fromList [(k, f k d (f k c (f k b a)))]
   

8. toList :: HashMap k v -> [(k, v)]

   unordered-containers	Data.HashMap.Strict

   Return a list of this map's elements. The list is produced lazily. The order of its elements is unspecified.

9. fromList :: (Eq a, Hashable a) => [a] -> HashSet a

   unordered-containers	Data.HashSet

   Construct a set from a list of elements.

10. toList :: HashSet a -> [a]

    unordered-containers	Data.HashSet

    Return a list of this set's elements. The list is produced lazily.

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