[R] general help on R and factor in R and a few simple comment from a newbie

Gabor Grothendieck ggrothendieck at gmail.com
Mon May 1 00:27:46 CEST 2006

On 4/30/06, Guojun Zhu <shmilylemon at yahoo.com> wrote:
> Hi.  I am starting to learn R for a course project.  I
> am  relative OK c++ programer.  I found the R is very
> different.  I have read the "an introduction to R".  I
> have to say it is not very newbie friendly.  It does
> not explain many things clearly.  And unfortunately,
> there is not too much introductory materials available
> on-line.  I do not want to buy a book.

into google and you get the R home page.  On the left pane of that
under Documentation click on Other and from there click on
Contributed Documentation and there is a list of literally dozens
of different introductions.

Also google for
  zoonekynd R
for another online intro to R.

> For example, I found factor is a quite different
> concept.I cannot use it as a vector which I can
> somehow think as a 1-dimension array.  help(factor)
> does not help much to clear about the concept either.
> Also there are quite few basic concepts like the data
> structure of model, etc is far from clear for me.  Yet
> there is no general place I can look for there more
> general idea.
> help is a very interesting and useful function.
> However, I would say the content lacks some general
> idea.  I used to learn Mathematica, which is also a
> high-level tool by their help.  It is very
> comprehensive, yet well-organized with some general
> idea, some specific fundtion explanation and some
> functions about one topic.  For R's help, you get only
> the specific explanation for the perticular function,
> and no more related things.  I feel it is more like a
> reference for experienced user instead of some newbie.
> I know there should be some trick by R with some dense
> code for big work.  But unfortunately, I could not
> find many place to learn it.
> Now for a specific question,
> I use read.csv to read some data from an excel data
> file (about 30,000 line data).  Some columns has empty
> data, so NA was read.  But they were read in as a
> factor instead of vector.  I need to manipulate them
> later as a vector (for example standardizing by
> dividing with standard deviation, or derive a new
> column from other two or more columns).  How to
> convert it into vector? Or maybe some functions
> already exists for factor already?

Check out the na.strings= and possibly the as.is = TRUE
arguments on read.table.  Also the read.xls command
from the gdata package may be helpful.

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