Karl Ove Hufthammer wrote:
On Mon, 1 Mar 2010 11:02:59 +0100 Karl Ove Hufthammer <k...@huftis.org>
wrote:
* What were your biggest misconceptions or
stumbling blocks to getting up and running
with R?
Also I found it quite confusing that
One more thing that still trips me up sometimes. '$' works on data
frames but not on matrices (with dimnames/colnames). Even though the two
objects *look* exactly the same, '$' on one of them works while '$' on
the other gives a *very* confusing error message. Example:
d=head(iris[1:4])
d2=as.matrix(d)
d
d2
d$Sepal.Width
d2$Sepal.Width
Some functions output matrices where you would expect them to output
data frames, and then this problem occurs. (Is there a reason why '$'
could/should not be made to 'work' on matrices too?)
The reason for the difference is that data.frames are lists organized
into columns (so the $ handling comes from the list, where it means
"extract the component") whereas a matrix is a single vector displayed
in columns.
Of course, the problem is that a beginner only knows that they both look
the same. But I think the idea of a list is so fundamental to R that it
needs to be something learned pretty early, so I'd rather not blur the
distinction between dataframes and matrices.
Duncan Murdoch
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