On Sun, Jan 11, 2009 at 9:04 PM, Jörg Groß <joerg@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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