On Apr 18, 2010, at 7:50 PM, Jeff Brown 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.
?prop.table
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) ) )
Would have been polite to include:
require(plyr)
, , 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.
> dimnames(B) <- list(x0 = dimnames(B)[[1]], x4 = dimnames(B)[[2]],
x5=dimnames(B)[[3]])
> B
, , x5 = 1
x4
x0 1 2 3
0 1 0.5 0.6
1 0 0.5 0.4
, , x5 = 2
x4
x0 1 2 3
0 0.5714286 0 0
1 0.4285714 1 1
Thanks a lot,
Jeff
--
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http://n4.nabble.com/xtabs-of-proportions-and-naming-a-dimension-not-a-row-tp2015261p2015261.html
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