On Apr 9, 2012, at 12:32 PM, James Lenihan wrote:
I found this example in an Introductory R book in the chapter on
Matrices and
Arrays
The array is
m
[,1] [,2] [,3] [,4] [,5]
[1,] 0 12 13 8 20
[2,] 12 0 15 28 88
[3,] 13 15 0 6 9
[4,] 8 28 6 0 33
[5,] 20 88 9 33 0
The code is
#returns the minimum value of d[i,j], i !=j and the row attaining
#the minimum, for square symmetric d; no special policy on ties
Would you consider a more compact operation? That code seems very unR-
ish.
min( m[row(m) != col(m)] )
#[1] 6
which(m == min( m[row(m) != col(m)] ), arr.ind=TRUE)
#
row col
[1,] 4 3
[2,] 3 4
-------------------
c(min= min( m[row(m) != col(m)] ),
which(m == min( m[row(m) != col(m)] ), arr.ind=TRUE)[1,])
########
min row col
6 4 3
I suppose the question could be how to debug that code, in which case
you should be manually "stepping through" it to see what the values
are during the implicit loop.
mind <- function(d) {
n <- nrow(d)
# add a column to identify row number for apply()
dd <- cbind(d,1:n)
wmins <- apply(dd[-n,],1,imin)
# wins will be 2 X n, 1st row being indices and 2nd being values
i <- which.min(wmins[2,])
j <- wmins[1,i]
return(c(d[i,j],i,j))
}
#this finds the location, value of the minimum in a row x
imin <- function(x) {
lx <- length(x)
i <- x[lx] # original row number
j <-which.min(x[(x+1):(lx-1)])
k <- i+j
return(c(k,x[k]))
}
The result s/b
[1] 6 3 4
I am getting:
Warning messages:
1: In (x + 1):(lx - 1) :
numerical expression has 6 elements: only the first used
2: In (x + 1):(lx - 1) :
numerical expression has 6 elements: only the first used
3: In (x + 1):(lx - 1) :
numerical expression has 6 elements: only the first used
4: In (x + 1):(lx - 1) :
numerical expression has 6 elements: only the first used
I have check my typing a number of times.
Does anyone see an error?
Thanks,
Jim L.
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