On Sun, Jan 11, 2009 at 9:04 PM, Jörg Groß <jo...@licht-malerei.de> wrote:
> ...now I want to get the mean and sd, as long as the column is not of type
> factor.
> ...But how can I check this, if I don't know the column name?
>
...
> is.factor(d[1])
> produces "FALSE".
>
Try is.factor(d[[1]]). Remember that in R, x[...] selects a *subsequence*,
not an *element*. Only x[[...]] selects an element. What makes this
confusing to learn is that for vectors, a subsequence of length 1 is treated
the same as an element. But for lists, they are not the same thing.
You can iterate over the columns in various ways, e.g.
for (i in 1:length(d)) ... d[[i]] ...
for (i in names(d)) ... d[[i]] ...
>
> Only
> is.factor(d$x)
> gives the correct result.
>
Remember that
d$x == d[["x"]]
Hope this helps,
-s
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