>> Surely, you mean
>> 
>> list dlist = dummify(x, max(c))

> max(x)?  That wouldn't work for a list argument, would
it?  

> We could insist that dummify takes a series argument, not a
list.  
> That would be backward-incompatible but probably wouldn't disturb 
> anyone.

Of course, you are correct. I have a blind spot about max(series), etc because I automatically think of max(list), because that is the way Stata and other programs work. It is somewhat confusing to combine the two distinct usages in a single function, but I will get used to it.

But, with respect to Allin's point, I think that insisting that dummify should take a series argument isn't a bad idea, since it seems to me that creating multiple sets of dummy variables at one go can easily create confusion for the unwary user.

Gordon