[R] Query to find minimum value in a matrix in R

[PIKAL Petr]

Hi

you can follow logic of functions by using debug and see how they operate by inspecting objects evaluated within functions.

See
?debug

However it seems to me that your functions are quite complicated. If I understand correctly, they compute minimum value of upper part of matrix. If I am correct, this function does the same, is shorter, more understandable and extensible.

min.upper <- function(x) {
mm <- min(x[upper.tri(x)])
x[lower.tri(x)] <- NA
ind <- which(x==mm, arr.ind=TRUE)
c(mm, ind)
}

mat <- structure(c(0, 5, 9, 13, 5, 0, 10, 14, 9, 10, 0, 15, 13, 14,
15, 0), .Dim = c(4L, 4L), .Dimnames = list(NULL, c("col1", "col2",
"col3", "col4")))
min.upper(mat)
[1] 5 1 2

Cheers
Petr

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of susmita T
> Sent: Friday, September 16, 2016 2:09 PM
> To: r-help at r-project.org
> Subject: [R] Query to find minimum value in a matrix in R
>
> Hi,
> Good Morning! I am new to R and finding difficulty in understanding the
> code. Since few days I am stuck at single line of code which I am unable to
> understand.
> Though there may be number of logics to find min value. As a new beginner I
> am following a book and as it has the following code
>
> mind<-function(d)
> {
>       n<-nrow(d)
>       dd<-cbind(d,1:n)
>       wmins<-apply(dd[-n,],1,imin)
>       i<-which.min(wmins[2,])
>       j<-wmins[1,i]
>       return(c(d[i,j],i,j))
> }
> imin<-function(x)
> {
>       lx<-length(x)
>       i<-x[lx]
>       j<-which.min(x[(i+1):(lx-1)])
>       k<-i+j
>       return(c(k,x[k]))
> }
>
> So when executed this with mind(below matrix) I get
> 0     12      13      8       20
> 12    0       15      28      88
> 13    15      0       6       9
> 8     28      6       0       33
> 20    88      9       33      0
> the answer as 6 , row 3 column 4
>
> Due to the symmetry of the matrix , the skipping of the early part of row is
> done by using expression (x[(i+1):(lx-1)])..(which is in red color in the code
> shown above). I am unable to understand the line in red code and how it is
> implemented in the line 5(i.e wins)…(shown in pink color in the code above I
> have done necessary homework to understand but still finding it hard to get
> it. Please someone help.
>
>
>       [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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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