Hi:

Using the result of xtabs, use prop.table():

Example:
df <- data.frame (
      x1 = ceiling( runif( 20 ) * 3 ),
      x2 = ceiling( runif( 20 ) * 2 ),
      y = round( runif( 20 ) )
  )

# Get different numbers since your random seed was not specified...
(w <- with(df, xtabs(~ y + x1 + x2)))
, , x2 = 1

   x1
y   1 2 3
  0 1 1 1
  1 1 1 1

, , x2 = 2

   x1
y   1 2 3
  0 1 4 2
  1 3 2 2

>class(w)
# [1] "xtabs" "table"
dim(w)
# [1] 2 3 2

> prop.table(w, c(2, 3))  # Column proportions
, , x2 = 1

   x1
y           1         2         3
  0 0.5000000 0.5000000 0.5000000
  1 0.5000000 0.5000000 0.5000000

, , x2 = 2

   x1
y           1         2         3
  0 0.2500000 0.6666667 0.5000000
  1 0.7500000 0.3333333 0.5000000

> prop.table(w, c(1, 3))  # Row proportions
, , x2 = 1

   x1
y           1         2         3
  0 0.3333333 0.3333333 0.3333333
  1 0.3333333 0.3333333 0.3333333

, , x2 = 2

   x1
y           1         2         3
  0 0.1428571 0.5714286 0.2857143
  1 0.4285714 0.2857143 0.2857143

HTH,
Dennis

On Sun, Apr 18, 2010 at 4:50 PM, Jeff Brown <dopethatwantscash@yahoo.com>wrote:

>
> Hi,
>
> xtabs() creates a table of counts.  I want a table of proportions -- that
> is, I want to divide every vector (along a particular dimension) by its
> sum.
>
> The tiny example below does that.  The call to xtabs() creates a matrix "A"
> with dimensions ("x1","x2","y").  I transform "A" using aperm() and aaply()
> to get the matrix "B".  The problem: "B" has dimensions (<No name>, "x2",
> "x1").  How can I give (back) the name "y" to the dimension with no name in
> the matrix "B"?  (Unless I misunderstand something, dimnames() won't do it
> -- that lets me name the rows in a given dimension, but not the dimension
> itself.)
>
> > df <- data.frame (
> +       x1 = ceiling( runif( 20 ) * 3 ),
> +       x2 = ceiling( runif( 20 ) * 2 ),
> +       y = round( runif( 20 ) )
> + )
> >
> > attach( df )
> >       ( A <- xtabs( ~ y + x1 + x2 ) )
> , , x2 = 1
>
>   x1
> y   1 2 3
>  0 2 3 2
>  1 0 2 0
>
> , , x2 = 2
>
>   x1
> y   1 2 3
>  0 3 2 2
>  1 0 3 1
>
> > detach(df)
> > ( B <- aperm( aaply( A, 2:3, function (row) row / sum(row) ), c(3,1,2) )
> )
> , , x2 = 1
>
>   x1
>    1   2 3
>  0 1 0.6 1
>  1 0 0.4 0
>
> , , x2 = 2
>
>   x1
>    1   2         3
>  0 1 0.4 0.6666667
>  1 0 0.6 0.3333333
>
> > dimnames(B)
> [[1]]                                                   # This is the line
> that's bothering me.
> [1] "0" "1"
>
> $x1
> [1] "1" "2" "3"
>
> $x2
> [1] "1" "2"
>
> If there's an easier way to get xtabs() to provide proportions instead of
> counts, I'd like to know that, too.  But whether there is or is not, I'd
> like to know how to name a dimension.
>
> Thanks a lot,
> Jeff
> --
> View this message in context:
> http://n4.nabble.com/xtabs-of-proportions-and-naming-a-dimension-not-a-row-tp2015261p2015261.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org 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.
>

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