[R] Replicating output from a function

[Greg Snow]

The replicate function will run code multiple times and return the output as a list (or possibly something simplified).  You can then use lapply, sapply, or other tools to summarize those results.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of AC Del Re
> Sent: Wednesday, February 17, 2010 1:58 PM
> To: r-help at r-project.org
> Subject: [R] Replicating output from a function
> 
> Hi All,
> 
> I have a function that is used with data frames having multiple id's
> per row and it aggregates the data down to 1 id per row. It also
> randomly selects one of the within-id values of a variable (mod),
> which often differ within-id.  Assume this data frame (below) is much
> larger and I want to repeat this function, say 100 times, and then
> derive the mean values of r over those 100 replications. Is there an
> easy way to do this?  What about in more complex situations
> where the output is r, var(r),  wi, etc, and a mean of all output is
> desired,  e.g.:
> 
> id<-c(1,1,1,rep(4:12))
> n<-c(10,20,13,22,28,12,12,36,19,12, 15,8)
> r<-c(.68,.56,.23,.64,.49,-.04,.49,.33,.58,.18, .6,.21)
> mod1<-factor(c(1,2,2, rep(c(1,2,3),3)))
> mod2<-c(1,2,15,rep(3,9))
> datas<-data.frame(id,n,r,mod1,mod2)
> 
> # intermediate level fuction (courtesy of Hadley Wickham):
> 
> pick_one <- function(x) {
>  if (length(x) == 1) return(x)
>  sample(x, 1)
> }
> 
> 
> # Function that I want replicated 100 times:
> 
> cat_sum1 <- function(meta, mod) {
>  m <- meta
>  m$mod <- mod
>  meta <- ddply(m,  .(id),  summarize,  r = mean(r), n=mean(n),  mod =
> pick_one(mod))
>  meta$z  <- 0.5*log((1 + meta$r)/(1-meta$r))
>  meta$var.z <- 1/(meta$n-3)
>  meta$wi <-  1/meta$var.z
>  return(meta)
> }
> 
> # output from 1 run:
> 
>  cat_sum1(datas,datas$mod1)
>   id     r        n       mod           z      var.z           wi
> 1   1  0.49 14.33333   2  0.53606034 0.08823529 11.33333
> 2   4  0.64 22.00000   1  0.75817374 0.05263158 19.00000
> 3   5  0.49 28.00000   2  0.53606034 0.04000000 25.00000
> 4   6 -0.04 12.00000   3 -0.04002135 0.11111111  9.00000
> 5   7  0.49 12.00000   1  0.53606034 0.11111111  9.00000
> 6   8  0.33 36.00000   2  0.34282825 0.03030303 33.00000
> 7   9  0.58 19.00000   3  0.66246271 0.06250000 16.00000
> 8  10  0.18 12.00000   1  0.18198269 0.11111111  9.00000
> 9  11  0.60 15.00000   2  0.69314718 0.08333333 12.00000
> 10 12  0.21  8.00000   3  0.21317135 0.20000000  5.00000
> 
> Is there a way that I could get this to run multiple times
> (internally) and then output in a similar format as above but with the
> mean values from the multiple runs?
> 
> Any help is much appreciated!
> 
> AC
> 
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