[R] Seeking help with a simple loop construction

[Andy Bunn]

Does this do what you want?

foo.df <- data.frame(x = rnorm(12), y = runif(12), z = factor(rep(1:3,4)))
bar.mat <- matrix(NA,  nrow = ncol(foo.df)-1, ncol = nlevels(foo.df$z))
for(i in 1:(ncol(foo.df)-1))
{
    bar.mat[i,] <- xtabs(foo.df[,i] ~ foo.df$z)
}
bar.mat

There's probably a slicker way with apply...

HTH, Andy

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch]On Behalf Of Greg Blevins
> Sent: Monday, November 29, 2004 1:09 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Seeking help with a simple loop construction
> 
> 
> Hello,
> 
> I have a df, pp, with five variables:
> 
> > nobs(pp)
>   q10_1   q10_2   q10_3   q10_4 actcode 
>    1620    1620    1620    1620    1620 
> 
> I want to create a loop to run four xtabs (the first four 
> variables above by the fifth) and then store the results in a 
> matrix.  Below I make my intent clear by showing the output of 
> one xtab which is inserted into a matrix.
> 
> > a <- xtabs(q10_1 ~ actcode)
> > a
> actcode
>  1  2  3  4  5  6  7  8  9 10 
>  7 11  3 60 66 56 21 40  7  8 
> 
> > freq.mat <- matrix(0, 4, 10, byrow = TRUE)
> > freq.mat[1,] <- a
> > freq.mat
>      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
> [1,]    7   11    3   60   66   56   21   40    7     8
> [2,]    0    0    0    0    0    0    0    0    0     0
> [3,]    0    0    0    0    0    0    0    0    0     0
> [4,]    0    0    0    0    0    0    0    0    0     0
> ===============================================================
> I have spent a couple of hours searching the web and my texts but 
> continue to strike out in my attempts to construct a correct 
> formulation of this simple loop. Help would be appreciated.
> 
> Greg Blevins
> The Market Solutions Group, Inc.
> Windows XP
> R 2.0.1
> Pentium 4
> 512 memory
> 
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