[R] finding the most frequent row

[Uwe Ligges]

bogdan romocea wrote:

> Here's something that works. I'm sure there are better solutions (in
> particular the paste part - I couldn't figure out how to avoid typing
> a[i,1], ..., a[i,10]).
> 
> a <- matrix(nrow=1000,ncol=10)
> for (i in 1:1000)
> 	for (j in 1:10)
> 		a[i,j] <- sample(1:0,1)
> 
> b <- vector(mode="character")
> for (i in 1:1000)
> 	b[i] <- paste(a[i,1],a[i,2],a[i,3],a[i,4],a[i,5],
> 		a[i,6],a[i,7],a[i,8],a[i,9],a[i,10],sep="")
> 
> #the most frequent row
> table(b)[table(b) == max(table(b))]

You mean:

   a <- matrix(sample(0:1, 10000, replace = TRUE), 1000, 10)
   b <- apply(a, 1, paste, collapse="")
   tb <- table(b)
   tb[which.max(tb)]

The real problem is that paste() is slow compared to numerical 
calculations. I think there is a better solution somewhere in the 
archives (I cannot remind right now), so look up the archives, please.

Uwe Ligges





> HTH,
> b.
> 
> 
> -----Original Message-----
> From: Lisa Pappas [mailto:lisa.pappas at hci.utah.edu]
> Sent: Thursday, December 09, 2004 5:15 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] finding the most frequent row
> 
> 
> I am bootstrapping using a function that I have defined.  The
> "Statistic" of the function is an array of 10 numbers.  Therefore if
> I use 1000 replications,  the "t" matrix will have 1000 rows each of
> which is a bootstrap replicate of this 10 number array (10 columns). 
> Is there any easy way in R to determine which row appears the most
> frequently? 
> 
> Thanks,
> Lisa Pappas
> 
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