# Re: [R] Query to find minimum value in a matrix in R

```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-boun...@r-project.org] On Behalf Of susmita T
> Sent: Friday, September 16, 2016 2:09 PM
> To: r-help@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
>
>
>       [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> guide.html
> and provide commented, minimal, self-contained, reproducible code.

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