Chapter 17. Sequences vs. Arrays
Even though JSON supports arrays, JSONiq uses a different construct as its first class citizens: sequences. Any value returned by or passed to an expression is a sequence.
The main difference between sequences and arrays is that sequences are completely flat, meaning they cannot contain other sequences.
Since sequences are flat, expressions of the JSONiq language just concatenate them to form bigger sequences.
This is very useful to stream and optimize -- for example, the runtime of the Zorba engine is iterator-based.
Example 17.1. Flat sequences.
( (1, 2), (3, 4) )
Results:
1
2
3
4
Arrays on the other side can contain nested arrays, like in JSON.
Example 17.2. Nesting arrays.
[ [ 1, 2 ], [ 3, 4 ] ]
Results:
[ [ 1, 2 ], [ 3, 4 ] ]
Many expressions return single items - actually, they really return a singleton sequence, but a singleton sequence of one item is considered the same as the item itself.
Example 17.3. Singleton sequences.
This is different for arrays: a singleton array is distinct from its unique member, like in JSON.
Example 17.4. Singleton sequences.
An array is a single item. A (non-singleton) sequence is not. This can be observed by counting the number of items in a sequence.
Example 17.5. count() on an array.
count([ 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } ])
Results:
1
Example 17.6. count() on a sequence.
count( ( 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } ) )
Results:
4
Other than that, arrays and sequences can contain exactly the same members (atomics, arrays, objects).
Example 17.7. Members of an array.
[ 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } ]
Results:
[ 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } ]
Example 17.8. Members of a sequence.
( 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } )
Results:
1
"foo"
[ 1, 2, 3, 4 ]
{
"foo" : "bar"
}
Arrays can be converted to sequences, and vice-versa.
Example 17.9. Converting an array to a sequence.
[ 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } ][]
Results:
1
"foo"
[ 1, 2, 3, 4 ]
{
"foo" : "bar"
}
Example 17.10. Converting a sequence to an array.
[ ( 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } ) ]
Results:
[ 1, "foo", [ 1, 2, 3, 4 ], { "foo" : "bar" } ]
