delete! for PriorityQueue (#428)

* delete! for PriorityQueue
Closes #343

* Update test_priority_queue.jl

* Update priority-queue.md

* correct test for #343

docs/src/priority-queue.md

@@ -14,6 +14,7 @@ enqueue!(pq, k, v)        # insert the key k into pq with priority v
 enqueue!(pq, k=>v)        # (same, using Pairs)
 dequeue!(pq)              # remove and return the lowest priority key
 peek(pq)                  # return the lowest priority key without removing it
+delete!(pq, k)            # delete the mapping for the given key in a priority queue, and return the priority queue.
 ```
 
 `PriorityQueue` also behaves similarly to a `Dict` in that keys can be

src/priorityqueue.jl

@@ -313,6 +313,26 @@ function dequeue_pair!(pq::PriorityQueue, key)
     dequeue_pair!(pq)
 end
 
+"""
+    delete!(pq, key)
+Delete the mapping for the given key in a priority queue, and return the priority queue.
+# Examples
+```jldoctest
+julia> q = PriorityQueue(Base.Order.Forward, "a"=>2, "b"=>3, "c"=>1)
+PriorityQueue{String,Int64,Base.Order.ForwardOrdering} with 3 entries:
+  "c" => 1
+  "b" => 3
+  "a" => 2
+julia> delete!(q, "b")
+DataStructures.PriorityQueue{String,Int64,Base.Order.ForwardOrdering} with 2 entries:
+  "c" => 1
+  "a" => 2
+```
+"""
+function delete!(pq::PriorityQueue, key)
+    dequeue_pair!(pq, key)
+    pq
+end
 
 # Unordered iteration through key value pairs in a PriorityQueue
 iterate(pq::PriorityQueue) = iterate(pq.index)

test/test_priority_queue.jl

@@ -202,6 +202,13 @@ import Base.Order.Reverse
             @test dequeue_pair!(pq, 'b') == ('b'=>4)
             @test length(pq) == 3
         end
+
+        @testset "delete!" begin
+            pq = PriorityQueue(Base.Order.Forward, "a"=>2, "b"=>3, "c"=>1)
+            pq_out = delete!(pq, "b")
+            @test pq === pq_out
+            @test Set(collect(pq)) == Set(["a"=>2, "c"=>1])
+        end
     end
 
     @testset "LowLevelHeapOperations" begin