> I guess I could have been a little more authoritative: the code
> unique(a[sapply(b,function(x) which.min(abs(x-a)))]) is exactly what I need.
That method could be written as the following function
f0 <- function (a, b, unique = TRUE)
{
ret <- a[sapply(b, function(x) which.min(abs(x - a)))]
if (unique) {
ret <- unique(ret)
}
ret
}
If 'a' is in sorted order then I think the following, based on findInterval,
does the same thing in less time, especially when 'b' is longish.
If 'a' may not be sorted then add
f1 <- function (a, b, unique = TRUE)
{
leftI <- findInterval(b, a)
rightI <- leftI + 1
leftI[leftI == 0] <- 1
rightI[rightI > length(a)] <- length(a)
ret <- ifelse(abs(b - a[leftI]) < abs(b - a[rightI]), a[leftI], a[rightI])
if (unique) {
ret <- unique(ret)
}
ret
}
E.g.,
R> a <- sort(rnorm(1e6))
R> b <- sort(rnorm(1000))
R> system.time(r0 <- f0(a, b))
user system elapsed
4.88 3.48 8.36
R> system.time(r1 <- f1(a, b))
user system elapsed
0 0 0
R> identical(r0, r1)
[1] TRUE
If 'a' might be unsorted then add
if (is.unsorted(a)) a <- sort(a)
at the beginning. If the output must be in the same order as the original
'a' then use order(a) and subscript 'a' and 'ret' with its output.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
> Behalf
> Of Andras Farkas
> Sent: Tuesday, June 18, 2013 10:24 AM
> To: Bert Gunter
> Cc: R mailing list
> Subject: Re: [R] find closest value in a vector based on another vector values
>
> Bert,
>
> I guess I could have been a little more authoritative: the code
> unique(a[sapply(b,function(x) which.min(abs(x-a)))]) is exactly what I need.
> Thanks for the
> input, your comments helped us make the code better,
>
> Andras
>
>
> --- On Tue, 6/18/13, Bert Gunter <gunter.ber...@gene.com> wrote:
>
> > From: Bert Gunter <gunter.ber...@gene.com>
> > Subject: Re: [R] find closest value in a vector based on another vector
> > values
> > To: "Andras Farkas" <motyoc...@yahoo.com>
> > Cc: "Jorge I Velez" <jorgeivanve...@gmail.com>, "R mailing list" <r-help@r-
> project.org>
> > Date: Tuesday, June 18, 2013, 10:55 AM
> > Andras:
> >
> > No.
> > Using the a = c(1,8,9) and b = 2:3 that ** I posted
> > before**, you get
> > the single unique value of 1.
> >
> > Please stop guessing, think carefully about what you want to
> > do, and
> > **test** your code.
> >
> > -- Bert
> >
> > On Tue, Jun 18, 2013 at 7:41 AM, Andras Farkas <motyoc...@yahoo.com>
> > wrote:
> > > Bert,
> > >
> > > thanks... The values should not repeat themselves if
> > the same a is closest to all b, so probably aruns example
> > extended with a unique command works best?
> > >
> > > unique(a[sapply(b,function(x) which.min(abs(x-a)))])
> > >
> > > thanks,
> > >
> > > Andras
> > >
> > > --- On Tue, 6/18/13, Bert Gunter <gunter.ber...@gene.com>
> > wrote:
> > >
> > >> From: Bert Gunter <gunter.ber...@gene.com>
> > >> Subject: Re: [R] find closest value in a vector
> > based on another vector values
> > >> To: "Jorge I Velez" <jorgeivanve...@gmail.com>
> > >> Cc: "Andras Farkas" <motyoc...@yahoo.com>,
> > "R mailing list" <r-help@r-project.org>
> > >> Date: Tuesday, June 18, 2013, 10:07 AM
> > >> Jorge: No.
> > >>
> > >> > a <-c(1,5,8,15,32,33.5,69)
> > >> > b <-c(8.5,33)
> > >> > a[findInterval(b, a)]
> > >> [1] 8 32 ##should be
> > >> 8 33.5
> > >>
> > >> I believe it has to be done explicitly by finding
> > all the
> > >> differences
> > >> and choosing those n with minimum values, depending
> > on what
> > >> n you
> > >> want.
> > >>
> > >> Note that the problem is incompletely specified.
> > What if the
> > >> same
> > >> value of a is closest to several values of b? -- do
> > you want
> > >> all the
> > >> values you choose to be different or not, in which
> > case they
> > >> may not
> > >> be minimum?
> > >>
> > >> a <- c(1, 8, 9)
> > >> b <- c(2,3)
> > >>
> > >> Then what are the 2 closest values of a to b?
> > >>
> > >> -- Bert
> > >>
> > >> On Tue, Jun 18, 2013 at 5:43 AM, Jorge I Velez
> > <jorgeivanve...@gmail.com>
> > >> wrote:
> > >> > Dear Andras,
> > >> >
> > >> > Try
> > >> >
> > >> >> a[findInterval(b, a)]
> > >> > [1] 8 32
> > >> >
> > >> > HTH,
> > >> > Jorge.-
> > >> >
> > >> >
> > >> > On Tue, Jun 18, 2013 at 10:34 PM, Andras
> > Farkas <motyoc...@yahoo.com>
> > >> wrote:
> > >> >
> > >> >> Dear All,
> > >> >>
> > >> >> would you please provide your thoughts on
> > the
> > >> following:
> > >> >> let us say I have:
> > >> >>
> > >> >> a <-c(1,5,8,15,32,69)
> > >> >> b <-c(8.5,33)
> > >> >>
> > >> >> and I would like to extract from "a" the
> > two values
> > >> that are closest to
> > >> >> the values in "b", where the length of
> > this vectors
> > >> may change but b will
> > >> >> allways be shorter than "a". So at the end
> > based on
> > >> this example I should
> > >> >> have the result "f" as
> > >> >>
> > >> >> f <-c(8,32)
> > >> >>
> > >> >> appreciate the help,
> > >> >>
> > >> >> Andras
> > >> >>
> > >> >>
> > ______________________________________________
> > >> >> R-help@r-project.org
> > >> mailing list
> > >> >> https://stat.ethz.ch/mailman/listinfo/r-help
> > >> >> PLEASE do read the posting guide
> > >> >> http://www.R-project.org/posting-guide.html
> > >> >> and provide commented, minimal,
> > self-contained,
> > >> reproducible code.
> > >> >>
> > >> >
> > >> >
> > [[alternative
> > >> HTML version deleted]]
> > >> >
> > >> >
> > ______________________________________________
> > >> > R-help@r-project.org
> > >> mailing list
> > >> > https://stat.ethz.ch/mailman/listinfo/r-help
> > >> > PLEASE do read the posting guide
> > >> > http://www.R-project.org/posting-guide.html
> > >> > and provide commented, minimal,
> > self-contained,
> > >> reproducible code.
> > >>
> > >>
> > >>
> > >> --
> > >>
> > >> Bert Gunter
> > >> Genentech Nonclinical Biostatistics
> > >>
> > >> Internal Contact Info:
> > >> Phone: 467-7374
> > >> Website:
> > >> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-
> biostatistics/pdb-ncb-home.htm
> > >>
> >
> >
> >
> > --
> >
> > Bert Gunter
> > Genentech Nonclinical Biostatistics
> >
> > Internal Contact Info:
> > Phone: 467-7374
> > Website:
> > http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-
> biostatistics/pdb-ncb-home.htm
> >
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
