On Mar 28, 2011, at 12:38 AM, Daniel Stutzbach wrote: > On Sun, Mar 27, 2011 at 10:53 PM, Nick Coghlan <ncogh...@gmail.com> wrote: > On Mon, Mar 28, 2011 at 2:11 PM, Daniel Stutzbach <stutzb...@google.com> > wrote: > > Is there a good use-case for the func argument? > > The examples that Raymond gives in the docs (cumulative > multiplication, running min/max, cash flow accumulation) look fairly > solid to me. > > (I had the nagging suspicion that I was making a blunder in my email, but I > couldn't see it despite rereading my email several times before sending. My > blunder was in not rereading the patch to see the examples. Anyway...) > > When would a running product, min, or max be useful?
There's no need to speculate. This API has long been present in other languages and libraries. Do a google code search for R's builtin functions cumsum, cumprod, cummin, and cummax. Look at mumpy's accumulate ufunc which works with many operators. APL and K also have an accumulate tool which takes arbitrary functions. Or consider as an API principle that there should be s useful default (addition in this case) and also hooks or parameters provided so that users don't have to do backflips to override hard-wired behaviors. Raymond
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