I've always thought that a "grid" collection type would be very useful. By "grid" I mean a combination of directory (or table) and array, so that I can have a 2-dimensional collection with headers like this (for example):
PersonNo  PersonName  City
AB123     Adams       New York
CD456     Jones       Denver
EF789     Smith       San Francisco
Of course, with the present set of collection classes, I can build this myself (and have done in the past), or use a directory with each column held as an array, etc.
This form of collection is very common in the user interface area, and is usually called a "grid". Indeed, ooDialog provides for just this (a ListView with multi-column and headers specified). And it would be nice if an ooRexx "grid" collection was available - say to pick a text file off a disk, then use it (e.g.) to populate a multi-column listview (assuming the file was in some appropriate format, e.g. with tabs separating each data value in a row).
The reason I built one of these myself some time ago, was that it was needed, and although I tried a directory with each index being a column header, and each  item being an array containing the column, I found this very difficult to work with, probably because I kept wanting to think of each *row* as an array, not each column.
Has anyone come across this as a requirement for ooRexx? Btw, I'm not trying to re-invent SQL.