[R] The most common row in a matrix?

[Petr Pikal]

Hi


On 20 Nov 2006 at 22:00, Atte Tenkanen wrote:

Date sent:      	Mon, 20 Nov 2006 22:00:01 +0200
From:           	Atte Tenkanen <attenka at utu.fi>
To:             	Bill.Venables at csiro.au, p.dalgaard at biostat.ku.dk
Priority:       	normal
Copies to:      	r-help at stat.math.ethz.ch
Subject:        	Re: [R] The most common row in a matrix?

> Many workable versions has been proposed. This mcr()-version seems to
> be fastest though it's not the shortest or at first sight the simplest
> among all. 
> 
> Is there any differences between unique and unique.matrices if the
> parameter is nxn-matrix?
> 
> By the way, what does 'drop=FALSE' means in function-command? It is
> not mentioned in help("function"). Is it some kind of more global
> parameter? Sorry all stupid questions, but my target is only to apply
> R, not to be a master ;-)
Try

 mat<-matrix(10,10,10)
 mat[,1]
 mat[,1, drop=F]

and see the difference. BTW it is on ?"[" help page.

HTH
Petr




> 
> Atte
> 
> > 
> > Here is an idea you can develop as you wish.  You need to be
> > specific about how to handly several rows that occur equally
> > commonly, for example.
> > 
> > mcr <- function(x, drop = FALSE) { #'most common row'
> >  xx <- do.call("paste", c(data.frame(x), sep = "\r"))
> >  tx <- table(xx)
> >  mx <- names(tx)[which(tx == max(tx))[1]]
> >  x[match(mx, xx), , drop = drop]
> > }
> > 
> > Slightly extend your example:
> > 
> > > x
> >     [,1] [,2] [,3] [,4] [,5]
> > [1,]    1    2    3    1    2
> > [2,]    2    3    1    2    3
> > [3,]    3    1    2    3    1
> > [4,]    1    2    3    1    2
> > [5,]    1    2    3    1    2
> > [6,]    2    3    1    2    3
> > [7,]    3    1    2    3    1
> > [8,]    1    2    3    1    2
> > 
> > Now:
> > 
> > > mcr(x)
> >     [,1] [,2] [,3] [,4] [,5]
> > [1,]    1    2    3    1    2
> > > mcr(x, drop = T)
> > [1] 1 2 3 1 2
> > 
> > ___
> > 
> > This kind of example suggests that it might be useful to make
> > 'match' generic (like 'duplicated' and 'unique'), with methods for
> > data frames and matrices.
> > 
> > Bill Venables.
> > 
> > -----Original Message-----
> > From: r-help-bounces at stat.math.ethz.ch
> > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of kone
> > Sent: Monday, 20 November 2006 5:31 AM
> > To: r-help at stat.math.ethz.ch
> > Subject: [R] The most common row in a matrix?
> > 
> > Hi,
> > 
> > How do you get the most common row from a matrix? If I have a 
> > matrix  
> > like this
> > 
> > array(1:3,dim=c(4,5))
> > 
> >      [,1] [,2] [,3] [,4] [,5]
> > [1,]    1    2    3    1    2
> > [2,]    2    3    1    2    3
> > [3,]    3    1    2    3    1
> > [4,]    1    2    3    1    2
> > 
> > in which rows 1 and 4 are similar, I want to find that vector c
> > (1,2,3,1,2).
> > 
> > Atte Tenkanen
> > University of Turku, Finland
> > 
> > ______________________________________________
> > 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
> > and provide commented, minimal, self-contained, reproducible code.
> > 
> >
> 
> ______________________________________________
> 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 and provide commented,
> minimal, self-contained, reproducible code.

Petr Pikal
petr.pikal at precheza.cz