Thinking through this, the reasons I use within:
1) Avoid chained [:=]
2) Better semantics than transform (i.e, avoid commas, have one large
expression block)
However, if i do:
X=within(X, {...}) #versus
transform(X)
is transform then more efficient?
I'm all for keeping consistency with data.frame, and I assume that's the
real reason these functions are here.
Perhaps this is really a case where we want an efficient multi-update
instead of a properly ordered within?
Or perhaps an overload on transform that allows {expr}.
On 5/28/2012 6:09 AM, Matthew Dowle wrote:
Not sure why but it seems to be consistent with base data.frame :
DF = data.frame(a=1:3,b=4:6)
within(DF,{c=a*b;d=a+b})
a b d c
1 1 4 5 4
2 2 5 7 10
3 3 6 9 18
I don't mind it being raised as a bug in data.table and we'll fix it and
and add to FAQ 2.17 as another difference to data.frame. Or maybe it
would be clearer to remove within.data.table(). Do we need it?
Matthew
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