On the PHPro.org website Kevin Waterson has posted a look at the AppendIterator iterator, a part of the SPL (Standard PHP Library) that is included with PHP5.
The SPL AppendIterator provides a method of iterating over multiple arrays at the same time. This can be very useful when aggregating data from different sources, such as XML or RSS feeds or even multiple database sources. The flexibility and efficiency of the whole SPL suite of tools is a the disposal of the AppendIterator making manipulating data in multiple objects fast and simple with a minimum of code.
His example shows what an AppendIterator object looks like, how to use it to add new values to an array and how to filter values out of the append process with a FilterIterator object.