[R] getting sapply to skip columns with non-numeric data?

[Liaw, Andy]

There's something that either you have not thought of or neglected to tell
us:  If you have k variables in the data frame, you will need a data frame
of k variables and one row to be able to rbind() to the bottom of the
original one.  What are you going to put in place for non-numeric variables?

Perhaps this might help:

R> dat <- data.frame(f=factor(1:3), x=3:5, y=6:4)
R> rbind(dat, as.data.frame(lapply(dat, function(x) if (!is.numeric(x)) NA
else mean(x))))
      f x y
1     1 3 6
2     2 4 5
3     3 5 4
11 <NA> 4 5

Andy 

From: r user
> 
> getting s-apply to skip columns with non-numeric data?
> I have a dataframe "x" of w columns.
> 
> Some columns are numeric, some are not.
> 
> I wish to create a function to calculate the mean and 
> standard deviation of each numeric column, and then "bind" 
> the column mean and standard deviation to the bottom of the dataframe.
> 
> e.g. 
> 
> tempmean <- apply(data.frame(x), 2, mean, na.rm = T) xnew <- 
> rbind(x,tempmean)
> 
> I am running into one small problem...what is the best way to 
> have sapply "skip" the non-numeric data and return NA's?
> 
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