Please use colMeans()! was: Re: [R] Calculate Mean of ColumnVectors?

[Dimitris Rizopoulos]

Hi Tom,

There is the "R Reference Card" by Tom Short and Rpad, which is 
extremely useful for a quick browsing of basic R functions. Check:

http://tolstoy.newcastle.edu.au/R/help/04/12/9637.html


For instance, colSums() and friends are in the "Matrices" section.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "Mulholland, Tom" <Tom.Mulholland at dpi.wa.gov.au>
To: <r-help at stat.math.ethz.ch>
Sent: Tuesday, January 11, 2005 9:51 AM
Subject: RE: Please use colMeans()! was: Re: [R] Calculate Mean of 
ColumnVectors?


> There are indeed speed advantages in using colSums etc. However the 
> disadvantage is that the newbie doesn't always find the power 
> inherent in the apply, sapply, tapply and mapply. For many things 
> that I do, the speed is the least of my worries; although I take the 
> point that using apply for means or sums in packages that are 
> distibuted to others is not the way to go.
>
> As many of us have found out (and I think it was in S Poetry) the 
> statement was made that vectorisation befuddles some beginners. So 
> learning how to use this command, on a nice easy topic such as 
> summing or averaging does have some merit. I have to admit using 
> colSums a lot, but I don't think I have ever thought to use 
> colMeans.
>
> As an aside; does anyone have a list of optimised functions. That is 
> functions like this one whose main benefit is speed (I think) I 
> guess many of us feel that we are constantly using hammers to crack 
> the nuts, but we still don't really know what's in the toolbox.
>
> Tom
>
>> -----Original Message-----
>> From: Uwe Ligges [mailto:ligges at statistik.uni-dortmund.de]
>> Sent: Tuesday, 11 January 2005 3:57 PM
>> To: r-help at stat.math.ethz.ch
>> Cc: 'Thomas Hopper'
>> Subject: Please use colMeans()! was: Re: [R] Calculate Mean of 
>> Column
>> Vectors?
>>
>>
>> Folks, please see ?colMeans (as already pointed out in at least one
>> message) and friends.
>> These are faster than those apply(X, 2, mean) calls
>> and please do use them when publishing code (both in packages
>> in on this
>> list).
>>
>> Uwe Ligges
>>
>>
>> >>Hello,
>> >>
>> >>I've got an array defined as y <- rnorm(3000), dim(y) <- c(3, 
>> >>1000).
>> >>
>> >>I'd like to produce a 1000-element vector z that is the mean of 
>> >>the
>> >>corresponding elements of y (like z[1,1] <- mean(y[1,1], y[2,1],
>> >>y[3,1])), but being new to R, I'm not sure how to do this for all
>> >>elements at once (or, at least, simply). Any help is appreciated.
>> >>
>> >>Thanks,
>> >>
>> >>Tom
>>
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>
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