R help - Dec 2003 - Easiest way to get the mean of a row of a data.frame?

Dear r-helpers!

I am kind of new to R.
I would like to calculate the mean of the numbers of this expression:

    data(USArrests)
    USArrests[row.names(M) == "Alabama",]

class() tells me it's a ``data.frame,'' what I actually desire is to
get
all numbers of a row as a vector or a list to let mean() calculate the mean
of the whole row.  (I know this doesn't make sense with USArrests, I just
used it here instead of my very own data.frame.)

Thank you very much!

Bye

Sven

rowMeans(mydf)  will do this for a data frame mydf.

Be careful though to use it only with all-numeric data frames (there is an
implicit as.matrix going on), and often it makes more sense to store such
data in a matrix.

apply(mydf, 1, mean) would also work, but is slower.

On Wed, 17 Dec 2003, Sven C. Koehler wrote:
> I am kind of new to R.
> I would like to calculate the mean of the numbers of this expression:
> 
>     data(USArrests)
>     USArrests[row.names(M) == "Alabama",]
> 
> class() tells me it's a ``data.frame,'' what I actually desire
is to get
> all numbers of a row as a vector or a list to let mean() calculate the mean
> of the whole row.  (I know this doesn't make sense with USArrests, I
just
> used it here instead of my very own data.frame.)
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

On Wed, Dec 17, 2003 at 08:27:41AM +0100, Sven C. Koehler
wrote:
> I am kind of new to R.
> I would like to calculate the mean of the numbers of this expression:
> 
>     data(USArrests)
>     USArrests[row.names(M) == "Alabama",]
> 
> class() tells me it's a ``data.frame,'' what I actually desire
is to get
> all numbers of a row as a vector or a list to let mean() calculate the mean
> of the whole row.  (I know this doesn't make sense with USArrests, I
just
> used it here instead of my very own data.frame.)
rowMeans(USArrest)

does what you want.

In case you want to do soemthing else but compute the mean you will find
this handy:

apply(USArrests, 1, mean)

here you can substitute "mean" by whatever function you'd like to
apply
to each row.

cu
	Philipp

-- 
Dr. Philipp Pagel                                Tel.  +49-89-3187-3675
Institute for Bioinformatics / MIPS              Fax.  +49-89-3187-3585
GSF - National Research Center for Environment and Health
Ingolstaedter Landstrasse 1
85764 Neuherberg, Germany