Why does implementing crossProduct with scala's iterators return an incorrect result?
Here I'm defining crossProduct as a function that should return tuples for all possible pairs of items from the left list with items from the right list.
object CrossProduct {
def crossProduct[A, B](left: TraversableOnce[A], right: TraversableOnce[B]): TraversableOnce[(A, B)] = {
for {
l <- left
r <- right
} yield (l, r)
}
def main(args: Array[String]): Unit = {
val left = Vector("A", "B", "C")
val right = Vector("1", "2", "3", "4")
println("With Vector, Vector")
crossProduct(left, right).foreach(println)
println("With Iterator, Vector")
crossProduct(left.toIterator, right).foreach(println)
println("With Vector, Iterator")
crossProduct(left, right.toIterator).foreach(println)
println("With Iterator, Iterator")
crossProduct(left.toIterator, right.toIterator).foreach(println)
}
}
When I pass in a vector as the right argument, it returns the correct results. When I pass in an iterator as the right argument, it fails to iterate to the second element of the left argument. Why is this happening?
With Vector, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Iterator, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Vector, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
With Iterator, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
scala iterator
asked Jan 3 at 5:40
moatramoatra
40849
add a comment |
Here I'm defining crossProduct as a function that should return tuples for all possible pairs of items from the left list with items from the right list.
object CrossProduct {
def crossProduct[A, B](left: TraversableOnce[A], right: TraversableOnce[B]): TraversableOnce[(A, B)] = {
for {
l <- left
r <- right
} yield (l, r)
}
def main(args: Array[String]): Unit = {
val left = Vector("A", "B", "C")
val right = Vector("1", "2", "3", "4")
println("With Vector, Vector")
crossProduct(left, right).foreach(println)
println("With Iterator, Vector")
crossProduct(left.toIterator, right).foreach(println)
println("With Vector, Iterator")
crossProduct(left, right.toIterator).foreach(println)
println("With Iterator, Iterator")
crossProduct(left.toIterator, right.toIterator).foreach(println)
}
}
When I pass in a vector as the right argument, it returns the correct results. When I pass in an iterator as the right argument, it fails to iterate to the second element of the left argument. Why is this happening?
With Vector, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Iterator, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Vector, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
With Iterator, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
scala iterator
asked Jan 3 at 5:40
moatramoatra
40849
add a comment |
Here I'm defining crossProduct as a function that should return tuples for all possible pairs of items from the left list with items from the right list.
object CrossProduct {
def crossProduct[A, B](left: TraversableOnce[A], right: TraversableOnce[B]): TraversableOnce[(A, B)] = {
for {
l <- left
r <- right
} yield (l, r)
}
def main(args: Array[String]): Unit = {
val left = Vector("A", "B", "C")
val right = Vector("1", "2", "3", "4")
println("With Vector, Vector")
crossProduct(left, right).foreach(println)
println("With Iterator, Vector")
crossProduct(left.toIterator, right).foreach(println)
println("With Vector, Iterator")
crossProduct(left, right.toIterator).foreach(println)
println("With Iterator, Iterator")
crossProduct(left.toIterator, right.toIterator).foreach(println)
}
}
When I pass in a vector as the right argument, it returns the correct results. When I pass in an iterator as the right argument, it fails to iterate to the second element of the left argument. Why is this happening?
With Vector, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Iterator, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Vector, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
With Iterator, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
scala iterator
asked Jan 3 at 5:40
moatramoatra
40849
Here I'm defining crossProduct as a function that should return tuples for all possible pairs of items from the left list with items from the right list.
object CrossProduct {
def crossProduct[A, B](left: TraversableOnce[A], right: TraversableOnce[B]): TraversableOnce[(A, B)] = {
for {
l <- left
r <- right
} yield (l, r)
}
def main(args: Array[String]): Unit = {
val left = Vector("A", "B", "C")
val right = Vector("1", "2", "3", "4")
println("With Vector, Vector")
crossProduct(left, right).foreach(println)
println("With Iterator, Vector")
crossProduct(left.toIterator, right).foreach(println)
println("With Vector, Iterator")
crossProduct(left, right.toIterator).foreach(println)
println("With Iterator, Iterator")
crossProduct(left.toIterator, right.toIterator).foreach(println)
}
}
When I pass in a vector as the right argument, it returns the correct results. When I pass in an iterator as the right argument, it fails to iterate to the second element of the left argument. Why is this happening?
With Vector, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Iterator, Vector
(A,1)
(A,2)
(A,3)
(A,4)
(B,1)
(B,2)
(B,3)
(B,4)
(C,1)
(C,2)
(C,3)
(C,4)
With Vector, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
With Iterator, Iterator
(A,1)
(A,2)
(A,3)
(A,4)
scala iterator
scala iterator
asked Jan 3 at 5:40
moatramoatra
40849
asked Jan 3 at 5:40
moatramoatra
40849
asked Jan 3 at 5:40
moatramoatra
40849
asked Jan 3 at 5:40
moatramoatra
40849
asked Jan 3 at 5:40
moatramoatra
40849
40849
add a comment |
add a comment |
1 Answer
1
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oldest
votes
Because an Iterator is traversable once and only once.
When left goes to its next element, right has to start over from the beginning. An Iterator can't do that. After a single traversal it is empty.
answered Jan 3 at 5:46
jwvhjwvh
28k52141
add a comment |
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1 Answer
1
active
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votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Because an Iterator is traversable once and only once.
When left goes to its next element, right has to start over from the beginning. An Iterator can't do that. After a single traversal it is empty.
answered Jan 3 at 5:46
jwvhjwvh
28k52141
add a comment |
Because an Iterator is traversable once and only once.
When left goes to its next element, right has to start over from the beginning. An Iterator can't do that. After a single traversal it is empty.
answered Jan 3 at 5:46
jwvhjwvh
28k52141
add a comment |
Because an Iterator is traversable once and only once.
When left goes to its next element, right has to start over from the beginning. An Iterator can't do that. After a single traversal it is empty.
answered Jan 3 at 5:46
jwvhjwvh
28k52141
Because an Iterator is traversable once and only once.
When left goes to its next element, right has to start over from the beginning. An Iterator can't do that. After a single traversal it is empty.
answered Jan 3 at 5:46
jwvhjwvh
28k52141
answered Jan 3 at 5:46
jwvhjwvh
28k52141
answered Jan 3 at 5:46
jwvhjwvh
28k52141
answered Jan 3 at 5:46
jwvhjwvh
28k52141
28k52141
add a comment |
add a comment |
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