Getting a list of unique values from a field

Justin_ODell

I'm trying to retrieve a list of unique values from a particular field in a layer using ArcObjects.

I was using the IDataStatistics.UniqueValues, but it causes the results to be corrupted as soon as the function is exited (in ArcMap 10.2+).  I think it's related to some longstanding issues with IDataStatistics (Issues with ArcObjects and ArcGIS 10.1 SP1 IDataStatistics  as an example).

I tried using the DISTINCT prefix on the IQueryFilterDefinition2, per the end of the discussion on the last thread, but couldn't get it to work on a shapefile -- It did work on the same data in a File Geodatabase.  What are the limitations of IQueryFilterDefinition2?  Have any other suggestions to get a list of unique values quickly?

Some Caveats:

• It's for commercial software and needs to support ArcMap 10.0-10.3.X
• We work with all flavors of GeoFeatureLayers and need to support shp, pgdb, fgdb, sde, etc.
• This function needs to run very quickly, because it's called every time the map refreshes (invalidates) and may be retrieving unique values from one column, from multiple layers with a large number of features each

ErinBrimhall

Hi Justin,

With regard to IDataStatistics.UniqueValues being corrupted, were you simply trying to return the value of this property (an IEnumerator instance) from your function?

Since IDataStatistics functionality is cursor-based, it's not entirely surprising that the contents of UniqueValues becomes corrupt once your function completes and the objects are out of scope.  You should consider copying the contents of the UniqueValues property to a separate variable (array, IList, or similar) and returning that from your function.