I have a matrix whose columns were filled with values which were functions
of cvseq<-seq(.2,.3,by=.1) (and a row value of mode integer). To do a lookup
for cv=.3 later, I wanted to match(.3,cvseq), which gave me NA, hence my
question. I thought R would match .3 in cvseq within .Machine$double.eps,
but I can understand it if .3 and the second element of cvseq would not have
identical bits.
Besides the helpful suggestions below, I also tried
> cvseqf <- as.factor(cvseq)
> match(.3,cvseq)
[1] 2
which worked.
In general, would it be better to go the enumeration route via as.factor or
the approximation route?
Thanks for the help.
-Dan
On Mon, Mar 16, 2009 at 8:24 AM, Stavros Macrakis <macra...@alum.mit.edu>wrote:
> Well, first of all, seq(from=.2,to=.3) gives c(0.2), so I assume you
> really mean something like seq(from=.2,to=.3,by=.1), which gives
> c(0.2, 0.3).
>
> %in% tests for exact equality, which is almost never a good idea with
> floating-point numbers.
>
> You need to define what exactly you mean by "in" for floating-point
> numbers. What sort of tolerance are you willing to allow?
>
> Some possibilities would be for example:
>
> approxin <- function(x,list,tol) any(abs(list-x)<tol) # absolute
> tolerance
>
> rapproxin <- function(x,list,tol) (x==0 && 0 %in% list) ||
> any(abs((list-x)/x)<=tol,na.rm=TRUE)
> # relative tolerance; only exact 0 will match 0
>
> Hope this helps,
>
> -s
>
> On Mon, Mar 16, 2009 at 9:36 AM, Daniel Murphy <chiefmur...@gmail.com>
> wrote:
> > Hello:I am trying to match the value 0.3 in the sequence seq(.2,.3). I
> get
> >> 0.3 %in% seq(from=.2,to=.3)
> > [1] FALSE
> > Yet
> >> 0.3 %in% c(.2,.3)
> > [1] TRUE
> > For arbitrary sequences, this "invisible .3" has been problematic. What
> is
> > the best way to work around this?
>
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