There are an infinite number of rules for which this might be an example, including:

- "keep only the first one"

- "delete only last one"

- "consolidate to the highest column and lowest type"

- "if the array size is odd numbered remove the last one, otherwise remove all those whose 11-bit checkdigit of the type doesn't match the 13-bit checksum of the current username",

and so on ad infinitum. For clarity can you tell us which of the possible rules you don't mean? (j/k).