Returns an iterator for all values from this iterator that pass a test.
THe given callback receives the value for each entry, its index, and the
iterator itself.
The callback is expected to return a truthy value if the entry is to be
retained.
The next method on the iterator will consume values from this iterator until
it finds a value that passes.
Returns an array with each value from this collection that passes the given test.
Returns an iterator for the respective return values of a callback for each value from this iteration.