R tricks

trickyR.R

# passArgsReplicate: how to pass additional named args as ... to function in replicate
passArgsReplicate <- function(n, func, ...){
  args = as.list(substitute(list(...)))[-1L]
  replicate(n = n,expr = do.call(func,args),simplify = FALSE)
}

# test calling and using global variables on different parallel processes
library(parallel)

parTest <- function(arg){
  x <<- sample(x = 10,size = 1)
  return(rnorm(n = x,mean = arg,sd = 1))
}

parOut = mclapply(1:10,parTest)

# what is an active binding and how do we use it?
# an active binding is like a standard variable but it will update its value every time it is accessed (ie; it is not static).
# in this example "getMyValue" will tell us how many rows are in "xx", note that if we change xx, so does the value "getMyValue" returns.
makeActiveBinding("getMyValue", function(){nrow(xx)}, .GlobalEnv)
xx = matrix(0,nrow = sample(100,1),ncol = 2)
getMyValue

# the versitality of the switch statement.
xx = function(x){
    switch(x,
           f = {return(rnorm(10))},
           {print("not f")}
     )  
}