[R] counting row repetitions without loop

[Doran, Harold]

Sorry, word wrap made that incomprehensible, I think

x  y
4  5
6  7
6  6
7  5
5  7
6  7
4  5
6  7
7  6
5  6
dat <- read.table('clipboard', header=TRUE)

dat$patt <- paste(dat$x,dat$y, sep='')

mm <- as.data.frame(with(dat, table(patt)))

dat <- merge(dat, mm, by='patt')

mat <- matrix(0, ncol=10, nrow=10)

gg <- matrix(c(dat$x, dat$y), ncol=2)

mat[gg] <- dat$Freq 

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Doran, Harold
> Sent: Wednesday, February 06, 2008 9:56 AM
> To: Waterman, DG (David); r-help at r-project.org
> Subject: Re: [R] counting row repetitions without loop
> 
> I think this does what you want, but there may be a more efficient way
> 
> x  y
> 4  5
> 6  7
> 6  6
> 7  5
> 5  7
> 6  7
> 4  5
> 6  7
> 7  6
> 5  6
> dat <- read.table('clipboard', header=TRUE) # copy sample 
> data above dat$patt <- paste(dat$x,dat$y, sep='') mm <- 
> as.data.frame(with(dat, table(patt))) dat <- merge(dat, mm, 
> by='patt') mat <- matrix(0, ncol=10, nrow=10) gg <- 
> matrix(c(dat$x, dat$y), ncol=2) mat[gg] <- dat$Freq 
> 
> > -----Original Message-----
> > From: r-help-bounces at r-project.org
> > [mailto:r-help-bounces at r-project.org] On Behalf Of Waterman, DG 
> > (David)
> > Sent: Wednesday, February 06, 2008 9:08 AM
> > To: r-help at r-project.org
> > Subject: [R] counting row repetitions without loop
> > 
> > Hi,
> >  
> > I have a data frame consisting of coordinates on a 10*10 grid, i.e.
> >  
> > > example
> >     x  y
> > 1   4  5
> > 2   6  7
> > 3   6  6
> > 4   7  5
> > 5   5  7
> > 6   6  7
> > 7   4  5
> > 8   6  7
> > 9   7  6
> > 10  5  6
> > 
> > What I would like to do is return an 10*10 matrix 
> consisting of counts 
> > at each position, so in the above example I would have a 
> matrix where, 
> > for example, cell [4,5] contains 2 and [6,7] contains 3. At 
> the moment 
> > I have implemented this using a for loop over the rows of the data 
> > frame, however the data frames I want to process are very 
> long so the 
> > loop takes many minutes to complete. Can I do this in a 
> more efficient 
> > way?
> >  
> > Cheers,
> > David
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> R-help at r-project.org mailing list
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> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>