Hello,
This is my solution. This is pretty fast (tested with a larger data set)! If
you have a more elegant way to do it (of similar speed), please reply.
Thanks for the help!
################## get highest and lowest values and names of a matrix
# create sample data
x <- swiss$Education[1:25]
dat = matrix(x,5,5)
colnames(dat) = c('a','b','c','d','e')
rownames(dat) = c('z','y','x','w','v')
#my solution
nms = dimnames(dat) #get matrix row and col names
cnt = 10 # number of max and mins to get
tmp = dat
mxs = list("list",cnt)
mns = list("list",cnt)
for(i in 1:cnt){
#get maxes
mx_dims = arrayInd(which.max(tmp), dim(tmp)) # get max dims for entire
matrix note: which.max also removes NA's
mx_nm = c(nms[[1]][mx_dims[1]],nms[[2]][mx_dims[2]]) #get names
mx = tmp[mx_dims] # get max value
mxs[[i]] = c(mx,mx_nm) # add max and dim names to list of maxes
tmp[mx_dims] = NA #removes last max so new one is found
#get mins (basically same as above)
mn_dims = arrayInd(which.min(tmp), dim(tmp))
mn_nm = c(nms[[1]][mn_dims[1]],nms[[2]][mn_dims[2]])
mn = tmp[mn_dims]
mns[[i]] = c(mn,mn_nm)
tmp[mn_dims] = NA
}
mxs
mns
# end
Regards,
Ben
On Tue, Oct 11, 2011 at 5:32 PM, "Dénes TÓTH" <tde...@cogpsyphy.hu> wrote:
>
> which.max is even faster:
>
> dims <- c(1000,1000)
> tt <- array(rnorm(prod(dims)),dims)
> # which
> system.time(
> replicate(100, which(tt==max(tt), arr.ind=TRUE))
> )
> # which.max (& arrayInd)
> system.time(
> replicate(100, arrayInd(which.max(tt), dims))
> )
>
> Best,
> Denes
>
> > But it's simpler and probably faster to use R's built-in capabilities.
> > ?which ## note the arr.ind argument!)
> >
> > As an example:
> >
> > test <- matrix(rnorm(24), nr = 4)
> > which(test==max(test), arr.ind=TRUE)
> > row col
> > [1,] 2 6
> >
> > So this gives the row and column indices of the max, from which row and
> > column names can easily be obtained from the dimnames attribute of the
> > matrix.
> >
> > Note: This assumes that the object in question is a matrix, NOT a data
> > frame, for which it would be slightly more complicated.
> >
> > -- Bert
> >
> >
> > On Tue, Oct 11, 2011 at 3:06 PM, Carlos Ortega
> > <c...@qualityexcellence.es>wrote:
> >
> >> Hi,
> >>
> >> With this code you can find row and col names for the largest value
> >> applied
> >> to your example:
> >>
> >> r.m.tmp<-apply(dat,1,max)
> >> r.max<-names(r.m.tmp)[r.m.tmp==max(r.m.tmp)]
> >>
> >> c.m.tmp<-apply(dat,2,max)
> >> c.max<-names(c.m.tmp)[c.m.tmp==max(c.m.tmp)]
> >>
> >> It's inmediate how to get the same for the smallest and build a function
> >> to
> >> calculate everything and return a list.
> >>
> >>
> >> Regards,
> >> Carlos Ortega
> >> www.qualityexcellence.es
> >>
> >> 2011/10/11 Ben qant <ccqu...@gmail.com>
> >>
> >> > Hello,
> >> >
> >> > I'm looking to get the values, row names and column names of the
> >> largest
> >> > and
> >> > smallest values in a matrix.
> >> >
> >> > Example (except is does not include the names):
> >> >
> >> > > x <- swiss$Education[1:25]
> >> > > dat = matrix(x,5,5)
> >> > > colnames(dat) = c('a','b','c','d','c')
> >> > > rownames(dat) = c('z','y','x','w','v')
> >> > > dat
> >> > a b c d c
> >> > z 12 7 6 2 10
> >> > y 9 7 12 8 3
> >> > x 5 8 7 28 12
> >> > w 7 7 12 20 6
> >> > v 15 13 5 9 1
> >> >
> >> > > #top 10
> >> > > sort(dat,partial=n-9:n)[(n-9):n]
> >> > [1] 9 10 12 12 12 12 13 15 20 28
> >> > > # bottom 10
> >> > > sort(dat,partial=1:10)[1:10]
> >> > [1] 1 2 3 5 5 6 6 7 7 7
> >> >
> >> > ...except I need the rownames and colnames to go along for the ride
> >> with
> >> > the
> >> > values...because of this, I am guessing the return value will need to
> >> be
> >> a
> >> > list since all of the values have different row and col names (which
> >> is
> >> > fine).
> >> >
> >> > Regards,
> >> >
> >> > Ben
> >> >
> >> > [[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.
> >> >
> >>
> >> [[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.
> >>
> >
> > [[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.
> >
>
> ______________________________________________
> 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.
>
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