Game of Life in R (abdridged)

life2.r

# Game of Life, by Vadim Vinichenko  https://github.com/vvinichenko
# I've pasted his 2 functions here with no experiment at the bottom in order to be able to source this code
# straight from R like this:
# source("http://raw.github.com/gist/1899814/881e5f92c9413a5e1800c8a274d177982d796a8c/life2.r")
# that line loads the 2 functions automatically. Experiment Gist to follow

shiftMatrix <- function(mx, dr, dc) {
	#Shift the matrix by dr (delta r) rows and dc columns
	#by adding e.g. dr rows of zeros and removing dr rows from the other side 
	
	nr <- nrow(mx)
	nc <- ncol(mx)
	
	#If the matrix is shifted by more than its nrow or ncol, we get a matrix of zeros 
	if (abs(dr) >= nr || abs(dc) >= nc) {
		mx <- matrix(0, nrow = nr, ncol = nc)
		return(mx)
	}
	
	#Rows:
	if (dr > 0) {
		mx <- rbind(mat.or.vec(dr, nc), mx)
		mx <- mx[1:nr,]
	} else if (dr < 0) {
		mx <- rbind(mx, mat.or.vec(-dr, nc))
		mx <- mx[(1 - dr):(nr - dr),]
	}
	
	#Columns:
	if (dc > 0) {
		mx <- cbind(mat.or.vec(nr, dc), mx)
		mx <- mx[,1:nc]
	} else if (dc < 0) {
		mx <- cbind(mx, mat.or.vec(nr, -dc))
		mx <- mx[,(1 - dc):(nc - dc)]
	}
	return(mx)
}

life_cycle <- function(mx) {
	#Move the board one generation forward
	
	mx0 <- matrix(0, nrow = nrow(mx), ncol = ncol(mx))
	
	#Produce 8 "shifted" boards and add them up
	for (n in (-1:1)) {
		for (m in (-1:1)) {
			if (n !=0 || m !=0) {
				mx0 <- mx0 + shiftMatrix(mx, n, m)
			}
		}
	}
	
	#Deaths and births
	mx[mx0 > 3 | mx0 < 2] <- 0
	mx[mx0 == 3] <- 1
	return(mx)
}