[R] crosstabulation of means

[Frank E Harrell Jr]

On Thu, 23 May 2002 13:56:52 -0400
"R. Heberto Ghezzo" <heberto.ghezzo at mcgill.ca> wrote:

> Hello, I am trying to print a crosttabulation of mean,sd,n for a
> continuous variable crossclassified by anoother/s grouping variables. I
> came up with:
> xtab2 <- function(x,g1,g2) {
>  funy <- function(z)
>    list(mean(z,na.rm=T),sd(z,na.rm=T),length(z))
>  aa <- by(x,list(g1,g2),funy)
>  bb <- matrix(unlist(aa),nrow=3
>    ,dimnames=list(c("mean","sd","n"),
>                 rep(levels(as.factor(g2)),
>                 rep(length(levels(as.factor(g1))),
>                     length(levels(as.factor(g2)))) ) ))
> }
> but as you can see the labels of the columns correspond only to the
> second factor, and if I try to generalize it to 3 grouping variables the
> thing does not work.
> Any suggestions please on how to write the dimnames paragraph
> appropriately?
> Thanks
>

There are many ways to do this.  One is to use functions in the Hmisc library:

s <- summarize(x, llist(g1,g2,g3,g4), smean.sd)  # smean.sd is in Hmisc: mean,sd

To make a nice table (but only up to 2 cross-classification variables) do:

summary(x ~ g1+g2, method='cross', fun=smean.sd)

The latter will include the Ns for each cell.

Frank Harrell
 
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-- 
Frank E Harrell Jr              Prof. of Biostatistics & Statistics
Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences
U. Virginia School of Medicine  http://hesweb1.med.virginia.edu/biostat
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