nkpartitions <- function(n, k, exact=FALSE, print=FALSE) { # n objects # k subgroups # exactly k or at most k? # print results as they are found?
if (n != floor(n) | n<=0) stop("n must be positive integer") if (k != floor(k) | k<=0) stop("k must be positive integer") if (print) { printnkp <- function(a) { for (j in seq(max(a))) cat("{", seq(along=a)[a==j], "} "); cat("\n") } } # How many? Stirling2nd <- function(n, k) { sum((-1)^seq(0,k-1) * choose(k, seq(0,k-1)) * (k-seq(0,k-1))^n) / factorial(k) } rows <- Stirling2nd(n,k) if (!exact & k>1) { for (i in seq(k-1,1)) { rows <- rows + Stirling2nd(n,i) } } if (print) cat("rows =",rows,"\n") # Allocate space theparts <- matrix(NA, nrow=rows, ncol=n) # begin counting howmany <- 0 # all in one group a <- rep(1,n) # does this count? if (!exact | (k==1)) { # increase count, store, and print howmany <- howmany + 1 theparts[howmany,] <- a if (print) printnkp(a) } # search for others repeat { # start at high end last <- n repeat { # increment it if possible if ((a[last] <= max(a[1:(last-1)])) & (a[last] < k)) { a[last] <- a[last]+1 # does this count? if (!exact | max(a)==k) { # increase count, store, and print howmany <- howmany + 1 theparts[howmany,] <- a if (print) printnkp(a) } # start again at high end. break } # otherwise set to 1 and move to a different object a[last] <- 1 if (last>2) { last <- last-1 next } # report the partitions return(theparts) } } } nkpartitions(5,3) nkpartitions(5,3,T) -- Dr Christopher Andrews University at Buffalo, Department of Biostatistics 242 Farber Hall [EMAIL PROTECTED] 716 829 2756 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html