[R] A Maze Generator

[Clint Bowman]

I'm familiar with mazes that have a designated starting and ending points
but don't see any here (or is this just a maze

Clint Bowman			INTERNET:	clint at ecy.wa.gov
Air Dispersion Modeler		INTERNET:	clint at math.utah.edu
Air Quality Program		VOICE:		(360) 407-6815
Department of Ecology		FAX:		(360) 407-7534

	USPS:  		PO Box 47600, Olympia, WA 98504-7600
	Parcels:	300 Desmond Drive, Lacey, WA 98503-1274

On Tue, 29 Apr 2008, McGehee, Robert wrote:

> Thanks! I wasn't on a clean R session so I didn't catch this. I intended the 'i' to be the same from the last for loop, but as you point out on the first run there is no 'i'!
>
> Try this:
>
> plotMaze <- function(z, text=FALSE, lwd=2, ...) {
>     N <- nrow(z)
>     y <- -matrix(rep(1:N, N), N, N, byrow=FALSE)-1
>     x <- matrix(rep(1:N, N), N, N, byrow=TRUE)
>     plot(1:(N+1), -1:-(N+1), type="n", ylab="", xlab="", axes=FALSE, ...)
>     segments(1, -1:-(N+1) , N+1, -1:-(N+1), lwd=lwd)
>     segments(1:(N+1), -1, 1:(N+1), -(N+1), lwd=lwd)
>     segments(x+(z==4), y+(z==3), x+(z!=2), y+(z!=1), col="white", lwd=lwd)
>     if (text) text(x+0.5, y+0.5, z)
>     rect(1, -1, N+1, -(N+1), lwd=lwd)
> }
>
>
> makeMaze <- function(N, p=1) {
>     z <- matrix(NA+0, N, N)
>     s <- function(x) if (length(x)==1) x else sample(x, size=1)
>     z[s(1:length(z))] <- 0
>     i <- 1
>     while (any(is.na(z))) {
>         xx <- list(z[c(2:N, N),],
>                    z[,c(1, 1:(N-1))],
>                    z[c(1, 1:(N-1)),],
>                    z[,c(2:N, N)])
>         xx[[1]][N,] <- NA; xx[[2]][,1] <- NA; xx[[3]][1,] <- NA; xx[[4]][,N] <- NA
>         prb <- rep(1, 4); prb[i] <- p
>         for (i in sample(1:4, prob=prb)) {
>             q <- !is.na(xx[[i]]) & is.na(z)
>             if (!any(q)) next
>             z[s(which(q))] <- i
>             break
>         }
>     }
>     z
> }
> set.seed(1)
> plotMaze(makeMaze(10), main="Simple Maze")
> plotMaze(makeMaze(25), main="Hard  Maze", lwd=1)
>
>
> -----Original Message-----
> From: Peter Dalgaard [mailto:p.dalgaard at biostat.ku.dk]
> Sent: Tuesday, April 29, 2008 5:34 PM
> To: McGehee, Robert
> Cc: r-help
> Subject: Re: [R] A Maze Generator
>
> McGehee, Robert wrote:
> > I had some fun this afternoon coding up a 'maze generator' in R. I
> > thought I'd pass along the fruits of my labor for everyone's amusement.
> >
> > As written, every point is connected to every other point, so feel free
> > to 'start' and 'finish' anywhere you like.
> >
> > Have fun!
> > --Robert
> >
> > PS. Feel free to pass along suggestions or comments.
> >
> >
> You have prb[i] <-p but no definition of i. What was intended?
>
>     -pd
> > ----------------------------------------------------------------
> > plotMaze <- function(z, text=FALSE, lwd=2, ...) {
> >     N <- nrow(z)
> >     y <- -matrix(rep(1:N, N), N, N, byrow=FALSE)-1
> >     x <- matrix(rep(1:N, N), N, N, byrow=TRUE)
> >     plot(1:(N+1), -1:-(N+1), type="n", ylab="", xlab="", axes=FALSE,
> > ...)
> >     segments(1, -1:-(N+1) , N+1, -1:-(N+1), lwd=lwd)
> >     segments(1:(N+1), -1, 1:(N+1), -(N+1), lwd=lwd)
> >     segments(x+(z==4), y+(z==3), x+(z!=2), y+(z!=1), col="white",
> > lwd=lwd)
> >     if (text) text(x+0.5, y+0.5, z)
> >     rect(1, -1, N+1, -(N+1), lwd=lwd)
> > }
> >
> >
> > makeMaze <- function(N, p=1) { # large 'p' may result in more order
> > plots
> >     z <- matrix(NA+0, N, N)
> >     s <- function(x) if (length(x)==1) x else sample(x, size=1)
> >     z[s(1:length(z))] <- 0
> >     while (any(is.na(z))) {
> >         xx <- list(z[c(2:N, N),],
> >                    z[,c(1, 1:(N-1))],
> >                    z[c(1, 1:(N-1)),],
> >                    z[,c(2:N, N)])
> >         xx[[1]][N,] <- NA; xx[[2]][,1] <- NA; xx[[3]][1,] <- NA;
> > xx[[4]][,N] <- NA
> >         prb <- rep(1, 4); prb[i] <- p
> >         for (i in sample(1:4, prob=prb)) {
> >             q <- !is.na(xx[[i]]) & is.na(z)
> >             if (!any(q)) next
> >             z[s(which(q))] <- i
> >             break
> >         }
> >     }
> >     z
> > }
> > set.seed(1)
> > plotMaze(makeMaze(10), main="Simple Maze")
> > plotMaze(makeMaze(25), main="Hard  Maze", lwd=1)
> >
> >
> > Robert McGehee, CFA
> > Geode Capital Management, LLC
> > One Post Office Square, 28th Floor | Boston, MA | 02109
> > Tel: 617/392-8396    Fax:617/476-6389
> > mailto:robert.mcgehee at geodecapital.com
> >
> >
> >
> > This e-mail, and any attachments hereto, are intended fo...{{dropped:11}}
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>
> --
>    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
>   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
>  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>