Re: [R] applying operations within() a matrix's environment

Fri, 04 Jul 2014 06:56:37 -0700 

No, I’m sorry.  That’s a mistake. I should have written:

row.active <- matrix(rbinom(K*steps, 1, .7), nr = K, nc = steps) == 1

so that this is a logical indexing vector, not just pulling out the first 
element. To avoid yielding NaNs (though that doesn’t really break the 
question), I’ve also changed the code slightly below

Thanks for pointing this out!

Steve

****
set.seed(1)
K <- 10
v1 <- rnorm(K)
v2 <- rnorm(K)
v3 <- rnorm(K)
steps <- 5
row.active <- matrix(rbinom(K*steps, 1, .7), nr = K, nc = steps)==1 ## changed

cbind(v1,v2,v3)

for(ii in 1:steps) {
    v1[row.active[,ii]] <- 2*v1[row.active[,ii]]
    v2[row.active[,ii]] <- 3*v3[row.active[,ii]]*(v1[row.active[,ii]]) # changed
    v3[row.active[,ii]] <- (v2[row.active[,ii]] + v3[row.active[,ii]] + 3)^2
}

cbind(v1,v2,v3)


Id like to be able to do this more succinctly with something like the 
following. This would also allow me to store all the variables in a matrix, 
which seems better than having so many variables (I actually have about 50).

v1 <- rnorm(K)
v2 <- rnorm(K)
v3 <- rnorm(K)
vars <- cbind(v1,v2,v3)

for(ii in 1:steps) {
    vars[row.active[,ii]] <- within(vars[row.active[,ii]], {
        v1 <- 2*v1
        v2 <- 3*v3*v1 # changed
        v3 <- (v2+v3 + 3)^2
    })
}


On Jul 4, 2014, at 2:51 AM, PIKAL Petr <petr.pi...@precheza.cz> wrote:

> Hi
>  
> Are you 100% sure that you always want select only first item from v1,v2 and 
> v3 and change it in each step of cycle and keep only last value from your 
> cycle in first item in vectors v1-3?
>  
> Because this is what your cycle does.
>  
> Petr
>  
> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On 
> Behalf Of Steve Bellan
> Sent: Friday, July 04, 2014 12:53 AM
> To: r-help@r-project.org
> Subject: [R] applying operations within() a matrix's environment
>  
> I am trying to optimize code for speed and readability for a fairly complex 
> function inside an MCMC sampler. As of now I have a bunch of variables inside 
> a function that get iteratively reset inside a loop. Something like this:
> 
> set.seed(1)
> K <- 10
> v1 <- rnorm(K)
> v2 <- rnorm(K)
> v3 <- rnorm(K)
> steps <- 5
> row.active <- matrix(rbinom(K*steps, 1, .7), nr = K, nc = steps)
> 
> cbind(v1,v2,v3)
> 
> for(ii in 1:steps) {
>     v1[row.active[,ii]] <- 2*v1[row.active[,ii]]
>     v2[row.active[,ii]] <- 3*v3[row.active[,ii]]^(v1[row.active[,ii]])
>     v3[row.active[,ii]] <- (v2[row.active[,ii]] + v3[row.active[,ii]] + 3)^2
> }
> 
> cbind(v1,v2,v3)
> 
> 
> Id like to be able to do this more succinctly with something like the 
> following. This would also allow me to store all the variables in a matrix, 
> which seems better than having so many variables (I actually have about 50).
> 
> v1 <- rnorm(K)
> v2 <- rnorm(K)
> v3 <- rnorm(K)
> vars <- cbind(v1,v2,v3)
> 
> for(ii in 1:steps) {
>     vars[row.active[,ii]] <- within(vars[row.active[,ii]], {
>         v1 <- 2*v1
>         v2 <- 3*v3^v1
>         v3 <- (v2+v3 + 3)^2
>     })
> }
> 
> But I get this error because with() & within() don�t work on objects that 
> aren�t environments such as matrices.
> 
> 
> > + . + Error in UseMethod("within") : 
>   no applicable method for 'within' applied to an object of class 
> "c('double', 'numeric�)"
> 
> 
> It�s important that I keep this as a matrix and not a data.frame or list 
> because I�m trying to optimize for speed.  Help is much appreciated. Thanks!
> 
> Steve
> 
> 
> Steve Bellan, PhD, MPH
> Post-doctoral Researcher
> Lauren Ancel Meyers Research Group
> Center for Computational Biology and Bioinformatics
> University of Texas at Austin
> http://www.bio.utexas.edu/research/meyers/steve_bellan/
> 
> 
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