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mapEitherWithKey :: (Key -> a -> Either b c) -> IntMap a -> (IntMap b, IntMap c)

containers	Data.IntMap.Lazy

Map keys/values and separate the Left and Right results.

let f k a = if k < 5 then Left (k * 2) else Right (a ++ a)
mapEitherWithKey f (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
== (fromList [(1,2), (3,6)], fromList [(5,"aa"), (7,"zz")])

mapEitherWithKey (\_ a -> Right a) (fromList [(5,"a"), (3,"b"), (1,"x"), (7,"z")])
== (empty, fromList [(1,"x"), (3,"b"), (5,"a"), (7,"z")])

mapKeys :: (Key -> Key) -> IntMap a -> IntMap a

containers Data.IntMap.Lazy

mapKeys f s is the map obtained by applying f to each key of s. The size of the result may be smaller if f maps two or more distinct keys to the same new key. In this case the value at the greatest of the original keys is retained.
```
mapKeys (+ 1) (fromList [(5,"a"), (3,"b")])                        == fromList [(4, "b"), (6, "a")]
mapKeys (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "c"
mapKeys (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "c"
```
mapKeysMonotonic :: (Key -> Key) -> IntMap a -> IntMap a

containers Data.IntMap.Lazy

mapKeysMonotonic f s == mapKeys f s, but works only when f is strictly monotonic. That is, for any values x and y, if x < y then f x < f y. The precondition is not checked. Semi-formally, we have:
```
and [x < y ==> f x < f y | x <- ls, y <- ls]
==> mapKeysMonotonic f s == mapKeys f s
where ls = keys s
```
This means that f maps distinct original keys to distinct resulting keys. This function has slightly better performance than mapKeys.
```
mapKeysMonotonic (\ k -> k * 2) (fromList [(5,"a"), (3,"b")]) == fromList [(6, "b"), (10, "a")]
```
mapKeysWith :: (a -> a -> a) -> (Key -> Key) -> IntMap a -> IntMap a

containers Data.IntMap.Lazy

mapKeysWith c f s is the map obtained by applying f to each key of s. The size of the result may be smaller if f maps two or more distinct keys to the same new key. In this case the associated values will be combined using c.
```
mapKeysWith (++) (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 1 "cdab"
mapKeysWith (++) (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")]) == singleton 3 "cdab"
```
Also see the performance note on fromListWith.

mapMaybe :: (a -> Maybe b) -> IntMap a -> IntMap b

containers	Data.IntMap.Lazy

Map values and collect the Just results.

let f x = if x == "a" then Just "new a" else Nothing
mapMaybe f (fromList [(5,"a"), (3,"b")]) == singleton 5 "new a"

mapMaybeWithKey :: (Key -> a -> Maybe b) -> IntMap a -> IntMap b

containers	Data.IntMap.Lazy

Map keys/values and collect the Just results.

let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"

mapWithKey :: (Key -> a -> b) -> IntMap a -> IntMap b

containers Data.IntMap.Lazy

Map a function over all values in the map.
```
let f key x = (show key) ++ ":" ++ x
mapWithKey f (fromList [(5,"a"), (3,"b")]) == fromList [(3, "3:b"), (5, "5:a")]
```
mapMaybeMissing :: forall (f :: Type -> Type) x y . Applicative f => (Key -> x -> Maybe y) -> WhenMissing f x y

containers Data.IntMap.Merge.Lazy

Map over the entries whose keys are missing from the other map, optionally removing some. This is the most powerful SimpleWhenMissing tactic, but others are usually more efficient.
```
mapMaybeMissing :: (Key -> x -> Maybe y) -> SimpleWhenMissing x y
```
```
mapMaybeMissing f = traverseMaybeMissing (\k x -> pure (f k x))
```
but mapMaybeMissing uses fewer unnecessary Applicative operations.
mapMissing :: forall (f :: Type -> Type) x y . Applicative f => (Key -> x -> y) -> WhenMissing f x y

containers Data.IntMap.Merge.Lazy

Map over the entries whose keys are missing from the other map.
```
mapMissing :: (k -> x -> y) -> SimpleWhenMissing x y
```
```
mapMissing f = mapMaybeMissing (\k x -> Just $ f k x)
```
but mapMissing is somewhat faster.
mapWhenMatched :: forall (f :: Type -> Type) a b x y . Functor f => (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b

containers Data.IntMap.Merge.Lazy

Map covariantly over a WhenMatched f x y.

containers	Data.IntMap.Merge.Lazy

containers	Data.IntMap.Merge.Lazy

containers	Data.IntMap.Merge.Lazy

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