[R] which() and value replacement in a matrix

[Patrick Giraudoux]

Thanks for the clue.

Actually the trouble comes when refering to a data.frame. If I use the matrix from the data.frame (matrix(mydataframe)), everything
goes smoothly...

So I wrote:

indices<-which(myforetbin > 0,arr.ind=T)
myforetbin<-as.matrix(myforetbin)
myforetbin[indices]<-1
myforetbin<-as.data.frame(myforetbin)

It works but I wonder if there are no more simple ways...

All the best,

Patrick


----- Original Message ----- 
From: "Liaw, Andy" <andy_liaw at merck.com>
To: "'Patrick Giraudoux'" <patrick.giraudoux at univ-fcomte.fr>; "r-help" <r-help at stat.math.ethz.ch>
Sent: Saturday, October 09, 2004 3:00 PM
Subject: RE: [R] which() and value replacement in a matrix


> Use the index vector directly, rather than breaking it up:
>
> > x <- matrix(sample(30), 10, 3)
> > idx <- which(x > 25, arr.ind=TRUE)
> > idx
>      row col
> [1,]   6   1
> [2,]   9   1
> [3,]   4   2
> [4,]   6   2
> [5,]   4   3
> > x[idx] <- 999
> > x
>       [,1] [,2] [,3]
>  [1,]    7   14   16
>  [2,]   20   24    8
>  [3,]   17   18   11
>  [4,]   19  999  999
>  [5,]   23    4   15
>  [6,]  999  999    5
>  [7,]   21    9   12
>  [8,]   22    2    3
>  [9,]  999   13    1
> [10,]    6   10   25
>
> HTH,
> Andy
>
> > From: Patrick Giraudoux
> >
> > Hi,
> >
> > I cannot go through the archives with which() as key-word...
> > so common. Though I am sure to have seen something about this subject
> > in the past could somebody put me on the track. I have a
> > matrix (actually a data.frame) in which I would replace the
> > non-null values
> > by 1.
> >
> > I tried the following:
> >
> > indices<-which(myforetbin > 0,arr.ind=T)
> > myforetbin[indices[,1],indices[,2]]<-1
> >
> > and get the message:
> >
> > > myforetbin[indices[,1],indices[,2]]<-1
> > Error in "[<-.data.frame"(`*tmp*`, indices[, 1], indices[,
> > 2], value = 1) :
> >         duplicate subscripts for columns
> >
> > I get the same with
> >
> > myforetbin[indices]<-1
> >
> > However, with:
> >
> > myforetbin[indices]
> >
> > I well get a vector with the corresponding non-null values.
> >
> > Can somebody put me on the track?
> >
> > All the best,
> >
> > Patrick
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide!
> > http://www.R-project.org/posting-guide.html
> >
> >
>
>
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