[R] 2D Random walk

[jim holtman]

This should work.  You have to return an object from a function; you
can not try to reference an object within a function.  So the value is
returned and saved in an object called 'rw' since that is how you are
referening it.


walk.2d<-function(n)
{
rw <- matrix(0, ncol = 2, nrow = n)

# generate the indices to set the deltas
indx <- cbind(seq(n), sample(c(1, 2), n, TRUE))

# now set the values
rw[indx] <- sample(c(-1, 1), n, TRUE)

# cumsum the columns
rw[,1] <- cumsum(rw[, 1])
rw[,2] <- cumsum(rw[, 2])

rw  # return value
}
n<-1000

rw <- walk.2d(n)
plot(0, type="n",xlab="x",ylab="y",main="Random Walk Simulation In
Two Dimensions",xlim=range(rw[,1]),ylim=range(rw[,2]))

        # use 'segments' to color each path
segments(head(rw[, 1], -1), head(rw[, 2], -1), tail(rw[, 1], -1), tail(rw[,
2], -1), col ="blue")


On Wed, Jun 29, 2011 at 11:30 AM, Komal <Komalsharif86 at gmail.com> wrote:
> HI Jholtman,
>
> walk.2d<-function(n)
> {
> rw <- matrix(0, ncol = 2, nrow = n)
>
> # generate the indices to set the deltas
> indx <- cbind(seq(n), sample(c(1, 2), n, TRUE))
>
> # now set the values
> rw[indx] <- sample(c(-1, 1), n, TRUE)
>
> # cumsum the columns
> rw[,1] <- cumsum(rw[, 1])
> rw[,2] <- cumsum(rw[, 2])
>
> return(rw[,1],rw[,2])
> }
> n<-1000
>
> plot(walk.2d(n), type="n",xlab="x",ylab="y",main="Random Walk Simulation In
> Two Dimensions",xlim=range(rw[,1]),ylim=range(rw[,2]))
>
>        # use 'segments' to color each path
> segments(head(rw[, 1], -1), head(rw[, 2], -1), tail(rw[, 1], -1), tail(rw[,
> 2], -1), col ="blue")
>
> I tried to make it in a function.. its not working I dont know why... please
> help me correcting this code.
>
> --
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>
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-- 
Jim Holtman
Data Munger Guru

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