如何在随机行走中包括计步器？

Question

In my random walk loop I need to incorporate a function that uses the step number as a variable.

How do I get R to produce a step number (loop counter may be a better term) during a random walk?

I need it right at the end of this code where I currently have the dummy code step.num

For reference my random walk code is:

    walkW <- function(n.times=125,
               xlim=c(524058,542800),
               ylim=c(2799758,2818500),
               start=c(542800,2815550),
               stepsize=c(4000,4000)) {

    plot(c(0,0),type="n",xlim=xlim,ylim=ylim,
           xlab="Easting",ylab="Northing",col="white",col.lab="white")#arena 
    x <- start[1]
    y <- start[2]
    steps <- 1/c(1,2,4,8,12,16)
    steps.y <- c(steps,-steps,0)
    steps.x <- c(steps[c(1,5,6)],-steps,0)
    points(x,y,pch=16,col="green",cex=1)

for (i in 1:n.times) {
        repeat {
           xi <- stepsize[1]*sample(steps.x,1)
           yi <- stepsize[2]*sample(steps.y,1)
           newx <- x+xi
           newy <- y+yi
           if (newx>xlim[1] && newx<xlim[2] &&
               newy>ylim[1] && newy<ylim[2]) break
        }
        lines(c(x,newx),c(y,newy),col="white")
         x <- newx
           y <- newy
}
  step.num<-(your magical step counter function) #I need the step counter here
 }

set.seed(101)
walkW(s)

Answer 1

After a for loop that was "broken", the index variable persists, so your magical code would just be:

 step.num <- i

Although for-loops are technically functions, sometimes they seem to have different scoping rules, and this is one such time. Your function returns the 'step.num' value, and after exit from walkW , you would not have been able to access 'i', but if the for-loop were done in the .GlobalEnv then the index "i" would still not have been reset or NULL-ed when the for-loop ended via break .