[R] sapply question

[Liaw, Andy]

Here's an example, using a data frame with two variables plus a grouping
factor:

> (dat <- data.frame(x1=1:10, x2=10:1, g=gl(2, 5)))
   x1 x2 g
1   1 10 1
2   2  9 1
3   3  8 1
4   4  7 1
5   5  6 1
6   6  5 2
7   7  4 2
8   8  3 2
9   9  2 2
10 10  1 2

Now, I want to compute 2 * x1 + x2 for each group in g:

> sapply(split(dat, dat$g), function(d) 2 * d$x1 + d$x2)
      1  2
[1,] 12 17
[2,] 13 18
[3,] 14 19
[4,] 15 20
[5,] 16 21

Does that help?

Andy 

From: Afshartous, David
> 
> Andy,
> My apologies for my very poor email.   Below is some simplified code.
> I think my confusion has more to do w/ embedding the sapplpy 
> within another function and returning the result, thus this 
> would apply to your "split" suggestion as well.
> However, when I run this the result is still empty.
> thanks!
> dave
> 
> 
> creatine.function.new.3 = function(dat) {
> result =  sapply(levels(dat$Patient_no), function(i) 
> 	{
> 		subdat <- subset(dat, dat$Patient_no==i)
> 		U = subdat$UV		 
> 		r = numeric(6)   
> 		for (i in 1:6) {		
> 			r[i] = 2*U[i]
> 		}
>        r  ## results for each patient
>        }
>        )
> result
> }
>  
> 
> -----Original Message-----
> From: Liaw, Andy [mailto:andy_liaw at merck.com] 
> Sent: Wednesday, June 28, 2006 10:23 AM
> To: Afshartous, David; r-help at stat.math.ethz.ch
> Subject: RE: [R] sapply question
> 
> If you attached files, none made it through the mailing list.
> 
> Can't you try posting a simplified version of the problem 
> instead?  Try
> to make it as easy for others to help you as possible will 
> maximize the
> chance you get some useful response.  Asking people to read 
> code you've
> attached in files isn't helping, especially if the code is 
> long and make
> use of data not accessible to anyone but you.
> 
> In general, if you want something like tapply, but need several
> variables instead of one, you can use something like:
> 
> sapply(split(dataFrame, factor_to_split_by), function(...))
> 
> HTH,
> Andy
> 
> From: Afshartous, David
> > 
> > sent this to the list yesterday but didn't see it listed in 
> the daily 
> > summary ... apologies if you receive it twice ...
> > 
> > ________________________________
> > 
> > From: Afshartous, David
> > Sent: Tuesday, June 27, 2006 10:02 AM
> > To: 'r-help at stat.math.ethz.ch'
> > Subject: sapply question
> > 
> > 
> > All:
> >  
> > I'm trying to use sapply to break up data within another function.
> > (tapply doens't seem to work since I want to access several 
> variables 
> > of a data set, not just break up a single variable according to a 
> > factor.) I tried the R documentation but that wasn't much help on 
> > this.
> >  
> > The first function in the attached file works, breaking up the data 
> > according to patient number (6 observations per 24 
> patients) via a for
> 
> > loop i=1,..24.
> >  
> > The second function is an attempt to use sapply instead of the first
> > "for loop".    
> > it doesn't load properly and I seem to be absolutely blind 
> as to why; 
> > my guess is that it's something "obvious".  any help appreciated.  
> > (necessary data
> > attached)
> >  
> > thanks!
> > dave
> >  
> > ps:
> > I'm on windows and,
> > r.2 =100  (input to function)
> > dat = comp.CAND.frm (attached file)
> > 
> > 
> > 	[[alternative HTML version deleted]]
> > 
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html
> > 
> > 
> 
> 
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