R help - Apr 2012 - filling the matrix row by row in the order from lower to larger elements

Hello, everybody!

I have a matrix "input" (see example below) - with all unique entries
that are actually unique ranks (i.e., start with 1, no ties).
I want to assign a value of 100 to the first row of the column that
contains the minimum (i.e., value of 1).
Then, I want to assign a value of 100 to the second row of the column
that contains the value of 2, etc.
The results I am looking for are in "desired.results".
My code (below) does what I need. But it's using a loop through all
the rows of my matrix and searches for a matrix element every time.
My actual matrix is very large. Is there a way to do it more efficiently?
Thank you very much for the tips!
Dimitri

input<-as.matrix(data.frame(a=c(5,1,3,7),b=c(2,6,4,8)))
(input)
desired.result<-as.matrix(data.frame(a=c(100,0,100,0),b=c(0,100,0,100)))
(desired.result)
result<-as.matrix(data.frame(a=c(0,0,0,0),b=c(0,0,0,0)))
for(i in 1:nrow(input)){ # i<-1
  mymin<-i
  mycoords<-which(input==mymin,arr.ind=TRUE)
  result[i,mycoords[2]]<-100
  input[mycoords]<-max(input)
}
(result)

-- 
Dimitri Liakhovitski

I maybe missing something but this seems like an indexing problem
which doesn't require a loop at all. Something like this maybe?

(input<-matrix(c(5,1,3,7,2,6,4,8),nc=2))
output <- matrix(0,max(input),2)
output[input[,1],1] <- 100
output[input[,2],2] <- 100
output

Cheers


On Fri, Apr 6, 2012 at 1:49 PM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
> Hello, everybody!
>
> I have a matrix "input" (see example below) - with all unique
entries
> that are actually unique ranks (i.e., start with 1, no ties).
> I want to assign a value of 100 to the first row of the column that
> contains the minimum (i.e., value of 1).
> Then, I want to assign a value of 100 to the second row of the column
> that contains the value of 2, etc.
> The results I am looking for are in "desired.results".
> My code (below) does what I need. But it's using a loop through all
> the rows of my matrix and searches for a matrix element every time.
> My actual matrix is very large. Is there a way to do it more efficiently?
> Thank you very much for the tips!
> Dimitri
>
> input<-as.matrix(data.frame(a=c(5,1,3,7),b=c(2,6,4,8)))
> (input)
> desired.result<-as.matrix(data.frame(a=c(100,0,100,0),b=c(0,100,0,100)))
> (desired.result)
> result<-as.matrix(data.frame(a=c(0,0,0,0),b=c(0,0,0,0)))
> for(i in 1:nrow(input)){ # i<-1
> ?mymin<-i
> ?mycoords<-which(input==mymin,arr.ind=TRUE)
> ?result[i,mycoords[2]]<-100
> ?input[mycoords]<-max(input)
> }
> (result)
>
> --
> Dimitri Liakhovitski
>
> ______________________________________________
> R-help at r-project.org 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.

I think the OP wants to fill values in an arbitrarily large matrix. 
Now, first of all, I'd like to know what his real problem is, since this 
seems like a very tedious and unproductive matrix to produce.  But in 
the meantime,  since he also left out important information, let's 
assume the input matrix is N rows by M columns, and that he wants 
therefore to end up with N instances of "100", not counting the
original
value of 100 that is one of his ranking values (a bad BAD move IMHO).

Then either loop or lapply over an equation like (I've expanded things 
more than necessary for clarity
result<-inmatrix
for (k in 1:N){
foo <- which (inmatrix == k,arr.ind=T)
result[k,foo[2]] <-100
}



I maybe missing something but this seems like an indexing problem
which doesn't require a loop at all. Something like this maybe?

(input<-matrix(c(5,1,3,7,2,6,4,8),nc=2))
output <- matrix(0,max(input),2)
output[input[,1],1] <- 100
output[input[,2],2] <- 100
output

Cheers


On Fri, Apr 6, 2012 at 1:49 PM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
 > Hello, everybody!
 >
 > I have a matrix "input" (see example below) - with all unique
entries
 > that are actually unique ranks (i.e., start with 1, no ties).
 > I want to assign a value of 100 to the first row of the column that
 > contains the minimum (i.e., value of 1).
 > Then, I want to assign a value of 100 to the second row of the column
 > that contains the value of 2, etc.
 > The results I am looking for are in "desired.results".
 > My code (below) does what I need. But it's using a loop through all
 > the rows of my matrix and searches for a matrix element every time.
 > My actual matrix is very large. Is there a way to do it more efficiently?
 > Thank you very much for the tips!
 > Dimitri
 >
 > input<-as.matrix(data.frame(a=c(5,1,3,7),b=c(2,6,4,8)))
 > (input)
 >
desired.result<-as.matrix(data.frame(a=c(100,0,100,0),b=c(0,100,0,100)))
 > (desired.result)
 > result<-as.matrix(data.frame(a=c(0,0,0,0),b=c(0,0,0,0)))
 > for(i in 1:nrow(input)){ # i<-1
 >  mymin<-i
 >  mycoords<-which(input==mymin,arr.ind=TRUE)
 >  result[i,mycoords[2]]<-100
 >  input[mycoords]<-max(input)
 > }
 > (result)
 >
-- 

Sent from my Cray XK6
"Quidvis recte factum, quamvis humile, praeclarum."

Ok, how's this:


Rgames> foo
      [,1] [,2] [,3] [,4]
[1,]    3    6    1   16
[2,]   10   14   12    5
[3,]   11    7   15    9
[4,]    8    4   13    2

Rgames> sapply(1:4,FUN=function(k){ 
foo[k,which(foo==k,arr.ind=T)[2]]<-100;return(foo)})->bar
Rgames> bar
       [,1] [,2] [,3] [,4]
  [1,]    3    3    3    3
  [2,]   10   10   10   10
  [3,]   11   11  100   11
  [4,]    8    8    8    8
  [5,]    6    6    6    6
  [6,]   14   14   14   14
  [7,]    7    7    7    7
  [8,]    4    4    4  100
  [9,]  100    1    1    1
[10,]   12   12   12   12
[11,]   15   15   15   15
[12,]   13   13   13   13
[13,]   16   16   16   16
[14,]    5  100    5    5
[15,]    9    9    9    9
[16,]    2    2    2    2


Rgames> rab<-matrix(apply(bar,1,max),4,4)
Rgames> rab
      [,1] [,2] [,3] [,4]
[1,]    3    6  100   16
[2,]   10   14   12  100
[3,]  100    7   15    9
[4,]    8  100   13    2


-- 

Sent from my Cray XK6
"Quidvis recte factum, quamvis humile, praeclarum."