Is this a reasonably fast way to do an approximate match of a vector x to
values in a list?

match.approx  <- function(x,list,tol=.0001)
    sapply(apply(abs(outer(list,x,"-"))<tol,2,which),"[",1)

Thanks.
-Dan

On Mon, Mar 16, 2009 at 8:24 AM, Stavros Macrakis <macrakis@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 <chiefmurphy@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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