R/combn2.R

In PSEA: Population-Specific Expression Analysis.

#identical to combn with third "if" statement commented out to prevent the transformation of x into seq(x) when x is an integer (28.01.2010)
combn2<-function (x, m, FUN = NULL, simplify = TRUE, ...)
{
    stopifnot(length(m) == 1L)
    if (m < 0)
        stop("m < 0")
    if (m == 0)
        return(if (simplify) vector(mode(x), 0L) else list())
#    if (is.numeric(x) && length(x) == 1L && x > 0 && trunc(x) ==
#        x)
#        x <- seq.int(x)
    n <- length(x)
    if (n < m)
        stop("n < m")
    m <- as.integer(m)
    e <- 0
    h <- m
    a <- 1L:m
    nofun <- is.null(FUN)
    if (!nofun && !is.function(FUN))
        stop("'FUN' must be a function or NULL")
    len.r <- length(r <- if (nofun) x[a] else FUN(x[a], ...))
    count <- as.integer(round(choose(n, m)))
    if (simplify) {
        dim.use <- if (nofun)
            c(m, count)
        else {
            d <- dim(r)
            if (length(d) > 1L)
                c(d, count)
            else if (len.r > 1L)
                c(len.r, count)
            else c(d, count)
        }
    }
    if (simplify) {
        out <- matrix(r, nrow = len.r, ncol = count)
    }
    else {
        out <- vector("list", count)
        out[[1L]] <- r
    }
    i <- 2L
    nmmp1 <- n - m + 1L
    while (a[1L] != nmmp1) {
        if (e < n - h) {
            h <- 1L
            e <- a[m]
            j <- 1L
        }
        else {
            e <- a[m - h]
            h <- h + 1L
            j <- 1L:h
        }
        a[m - h + j] <- e + j
        r <- if (nofun)
            x[a]
        else FUN(x[a], ...)
        if (simplify)
            out[, i] <- r
        else out[[i]] <- r
        i <- i + 1L
    }
    if (simplify)
        array(out, dim.use)
    else out
}