Group-By parameters are an important tool for effective FME data transformations.
FME transformers can carry out transformations on either one feature at a time, or on a whole set of features at once.
For example, the AreaCalculator transformer operates on one feature at a time (to measure the area of that one polygon feature).
The StatisticsCalculator is called a group-based transformer; it operates on multiple features at a time (to calculate an average value for them all).
In FME we call this set of features a group.
By default a group-based transformer treats ALL the features that it is fed as a single group.
However, such transformers also have a Group-By parameter. This parameter lets the user define several groups based upon the value of an attribute.
######Mr. Statistics-Calculator, CFO, says…
"To illustrate the point consider calculating the average age of everyone who uses FME. This is the default group.
Now divide everyone up on into men and women. You have made a set of two groups and can calculate average age per gender.
This is the same as having a gender attribute in a dataset and selecting that in an FME group-by parameter."
Here, a LineOnLineOverlayer transformer is being used to intersect a number of line features.
The selected Group-By attribute is name.
The result is a series of groups for overlaying where the features in each group share the same value for name.
The practical outcome is that intersection will only take place on line features with the same name.