See arrayIndex() in the R.utils package, e.g. X <- array((2*3*4):1, dim=c(2,3,4)) idx <- 1:length(X) ijk <- arrayIndex(idx, dim=dim(X)) print(ijk) [,1] [,2] [,3] [1,] 1 1 1 [2,] 2 1 1 [3,] 1 2 1 [4,] 2 2 1 [5,] 1 3 1 [6,] 2 3 1 [7,] 1 1 2 [8,] 2 1 2 [9,] 1 2 2 10,] 2 2 2 11,] 1 3 2 12,] 2 3 2 13,] 1 1 3 14,] 2 1 3 15,] 1 2 3 16,] 2 2 3 17,] 1 3 3 18,] 2 3 3 19,] 1 1 4 20,] 2 1 4 21,] 1 2 4 22,] 2 2 4 23,] 1 3 4 24,] 2 3 4 /Henrik On 8/16/07, Moshe Olshansky <m_olshansky at="" yahoo.com=""> wrote: > A not very good solution is as below: > > If your array's dimensions were KxMxN and the "linear" > index is i then > n <- ceiling(i/(K*M)) > i1 <- i - (n-1)*(K*M) > m <- ceiling(i1/K) > k <- i1 - (m-1)*K > > and your index is (k,m,n) > > I am almost sure that there is a function in R which > does this (it exists in Matlab). > > Regards, > > Moshe. > > --- Ana Conesa <aconesa at="" ochoa.fib.es=""> wrote: > > > Dear list, > > > > I am looking for a function/way to get the array > > coordinates of given > > elements in an array. What I mean is the following: > > - Let X be a 3D array > > - I find the ordering of the elements of X by ord <- > > order(X) (this > > returns me a vector) > > - I now want to find the x,y,z coordinates of each > > element of ord > > > > Can anyone help me? > > > > Thanks! > > > > Ana > > > > ______________________________________________ > > R-help at stat.math.ethz.ch 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 at stat.math.ethz.ch 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. >

If I am correctly understanding the problem, I think that this is what you want: set.seed(1) # Create a 3x3x3 array ARR <- array(sample(100, 27), c(3, 3, 3)) > ARR , , 1 [,1] [,2] [,3] [1,] 27 89 97 [2,] 37 20 62 [3,] 57 86 58 , , 2 [,1] [,2] [,3] [1,] 6 61 43 [2,] 19 34 88 [3,] 16 67 83 , , 3 [,1] [,2] [,3] [1,] 32 17 21 [2,] 63 51 29 [3,] 75 10 1 # Get the ordered indices of the elements in the array > order(ARR) [1] 27 10 24 12 22 11 5 25 1 26 19 14 2 16 23 3 9 13 8 20 15 21 [23] 18 6 17 4 7 # Get the actual array elements in order > ARR[order(ARR)] [1] 1 6 10 16 17 19 20 21 27 29 32 34 37 43 51 57 58 61 62 63 67 75 [23] 83 86 88 89 97 # Now loop over the above and using which(), get the 3D indices > t(sapply(ARR[order(ARR)], function(x) which(ARR == x, arr.ind = TRUE))) [,1] [,2] [,3] [1,] 3 3 3 [2,] 1 1 2 [3,] 3 2 3 [4,] 3 1 2 [5,] 1 2 3 [6,] 2 1 2 [7,] 2 2 1 [8,] 1 3 3 [9,] 1 1 1 [10,] 2 3 3 [11,] 1 1 3 [12,] 2 2 2 [13,] 2 1 1 [14,] 1 3 2 [15,] 2 2 3 [16,] 3 1 1 [17,] 3 3 1 [18,] 1 2 2 [19,] 2 3 1 [20,] 2 1 3 [21,] 3 2 2 [22,] 3 1 3 [23,] 3 3 2 [24,] 3 2 1 [25,] 2 3 2 [26,] 1 2 1 [27,] 1 3 1 See ?which and take note of the arr.ind argument. HTH, Marc Schwartz On Thu, 2007-08-16 at 19:21 -0700, Moshe Olshansky wrote: > A not very good solution is as below: > > If your array's dimensions were KxMxN and the "linear" > index is i then > n <- ceiling(i/(K*M)) > i1 <- i - (n-1)*(K*M) > m <- ceiling(i1/K) > k <- i1 - (m-1)*K > > and your index is (k,m,n) > > I am almost sure that there is a function in R which > does this (it exists in Matlab). > > Regards, > > Moshe. > > --- Ana Conesa <aconesa at="" ochoa.fib.es=""> wrote: > > > Dear list, > > > > I am looking for a function/way to get the array > > coordinates of given > > elements in an array. What I mean is the following: > > - Let X be a 3D array > > - I find the ordering of the elements of X by ord <- > > order(X) (this > > returns me a vector) > > - I now want to find the x,y,z coordinates of each > > element of ord > > > > Can anyone help me? > > > > Thanks! > > > > Ana > >

[Ana Conesa] > I am looking for a function/way to get the array coordinates of given > elements in an array. What I mean is the following: > - Let X be a 3D array > - I find the ordering of the elements of X by ord <- order(X) > (this returns me a vector) > - I now want to find the x,y,z coordinates of each element of ord [Moshe Olshansky] >If your array's dimensions were KxMxN and the "linear" >index is i then >n <- ceiling(i/(K*M)) >i1 <- i - (n-1)*(K*M) >m <- ceiling(i1/K) >k <- i1 - (m-1)*K >and your index is (k,m,n) The reshape package might be helpful, here. If I understand the problem correctly, given this artificial example: X <- sample(1:24) dim(X) <- c(2, 3, 4) you would want: library(reshape) melt(X)[order(X), -4] so getting the indices in a three columns data frame. -- Fran?ois Pinard http://pinard.progiciels-bpi.ca