List

From Fmepedia

Lists are FME's way of dealing with 1-to-many relationships by allowing one attribute to have multiple values. Several transformers, such as the Joiner and the various overlay transformers, will automatically create a list if necessary. This is often the case when attributes from various different features are grouped into a single feature.

There are several transformers that can be used to manipulate lists:

• ListBuilder
• ListConcatenator
• ListCopier
• ListDuplicateRemover
• ListElementCounter
• ListExploder
• ListHistogrammer
• ListIndexer
• ListPopulator
• ListRangeExtractor
• ListRemover
• ListSearcher
• ListSorter
• ListSummer

Few, if any at all, output formats offer no support for lists, or 1-to-many relationships, so if you want to output the data to such a format you'll need to deal with the list first.

It's recommended to remove lists, especially ones with many items, as soon as you are done with them. This will save memory and processing time and will reduce the clutter of your workbench.

Lists are indicated in workbench by their name, followed by a pair of curly brackets, e.g. mylist{}. A specific list element has its number between the brackets, e.g. mylist{0}. Attributes of a list element are shown like this: mylist{0}.myattribute

Not all list elements have attributes, sometimes a list element simply has a value, for example a list generated by the AttributeSplitter

In order to access specific list elements in the Workbench GUI, right click on a list (e.g. mylist{}) in the attribute list and choose "Expose elements". Then type in the number of elements you want to expose. Keep in mind that list elements start counting at 0, so exposing 1 element of mylist{} will result in the extra attribute mylist{0} being available.

List elements can have other lists as part of their attributes.