[R] Retrieving the 2 row of "dist" computations

[Bill.Venables at csiro.au]

This is a lazy way, and a slightly extravagant way if your memory is limited and you are dealing with large numbers of rows.

NCols <- 5
NRows <- 7 
myMat <- matrix(runif(NCols*NRows), ncol=NCols) 

d <- dist(myMat)

dm <- as.matrix(d)
diag(dm) <- Inf
ij <- which(dm == min(dm), arr.ind = TRUE)[1,] 
ij

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Jeff08
Sent: Thursday, 10 June 2010 1:30 PM
To: r-help at r-project.org
Subject: [R] Retrieving the 2 row of "dist" computations


Dear R Gurus,

As you probably know, dist calculates the distance between every two rows of
data. What I am interested in is the actual two rows that have the least
distance between them, rather than the numerical value of the distance
itself.

For example, If the minimum distance in the following sample run is d[14],
which is .3826119, and the rows are 4 & 6. I need to find a generic way to
retrieve these rows, for a generic matrix of NRows (in this example NRows=7)

NCols=5
NRows=7 
myMat<-matrix(runif(NCols*NRows), ncol=NCols) 

d<-dist(myMat)

          1         2         3         4         5         6
2 0.7202138                                                  
3 0.7866527 0.9052319                                        
4 0.6105235 1.0754259 0.8897555                              
5 0.5032729 1.0789359 0.9756421 0.4167131                    
6 0.6007685 0.6949224 0.3826119 0.7590029 0.7994574          
7 0.9751200 1.2218754 1.0547197 0.5681905 0.7795579 0.8291303

e<-sort.list(d)
e<-e[1:5]  ##Retrieve minimum 5 distances

[1] 14 16  4 18  5
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