high and lowest with names

Here is a more R'sh solution (speed unknown).

Courtesy of Mark Leeds (I
modified it a bit to generalize it for a cnt input and get min and  
max).
Again, getting cnt highest and lowest values in the entire matrix and
display the data point row and column names with each:

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')
cnt = 10
#===============================================
print(dat)

  a  b  c  d  e
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

# MAKE IT A VECTOR FOR EASIER ORDERING
datasvec <- as.vector(dat)
# ORDER IT
datasvecordered<- order(datasvec)
# RECYCLE ROWS AND COLUMNS NAMES FOR EASIER MAPPING
recycledcols <- rep(colnames(dat),each=nrow(dat))
recycledrows <- rep(rownames(dat),times=ncol(dat))

# GET THE VALUES, THE ROW NAMES AND THE COLUMN NAMES
len = length(datasvecordered)
rr_len = length(recycledrows)

rbind(datasvec[datasvecordered][(len- 
cnt):len],recycledrows[datasvecordered][(rr_len- 
cnt):rr_len],recycledcols[datasvecordered][(rr_len-cnt):rr_len])
    [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11]
[1,] "9"  "9"  "10" "12" "12" "12" "12" "13" "15" "20"  "28"
[2,] "y"  "v"  "z"  "z"  "y"  "w"  "x"  "v"  "v"  "w"   "x"
[3,] "a"  "d"  "e"  "a"  "c"  "c"  "e"  "b"  "a"  "d"   "d"

rbind(datasvec[datasvecordered][1:cnt],recycledrows[datasvecordered] 
[1:cnt],recycledcols[datasvecordered][1:cnt])
    [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] "1"  "2"  "3"  "5"  "5"  "6"  "6"  "7"  "7"  "7"
[2,] "v"  "z"  "y"  "x"  "v"  "z"  "w"  "w"  "z"  "y"
[3,] "e"  "d"  "e"  "a"  "c"  "c"  "e"  "a"  "b"  "b"

enjoy

ben

On Wed, Oct 12, 2011 at 11:47 AM, Ben qant <ccquant at gmail.com> wrote:

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, "D?nes T?TH" <tdenes at 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
<cof at 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 <ccquant at 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