R/stackPoints.R

In garrettgman/Visual-Inference-Tools: Visual Inference Tools

#' Calculates y values for a vector of overlapping x values. Y values are designed to prevent overlapping by creating the appearance of stacked data. A helper function for numeric 1d Data. Also used for 2d data where one dimension is numeric, and one is categorical.
stackPoints <- function(x, levels = rep(1, length(x)), vp, y.min = 0.3,
                        y.max = unit(1, "npc")) {
    if (length(x) <= 1) y.min
    else {
        if (is.numeric(y.max)) y.max <- unit(y.max, "npc")
        seekViewport(vp)
        y.max <- convertY(y.max, "npc", valueOnly = TRUE)
        pheight <- convertHeight(unit(1, "char"), "native",
                                 valueOnly = TRUE) * 0.8
        binwidth <- convertWidth(unit(1, "char"), "native",
                                 valueOnly = TRUE)
        upViewport(0)

        nbins <- ceiling(diff(range(x)) / binwidth)
        breaks <- min(x) + c(0:(nbins)) * binwidth
        group <- cut(x, breaks, include.lowest = TRUE)

        stack.y <- rep(NA, length(x))

        for (level in unique(levels)) {
            which.x <- which(levels == level)
            max.stack <- max(table(group[which.x]))
            ydist <- min(diff(c(y.min, y.max))/max.stack,
                         as.numeric(pheight))
            df <- data.frame(x = x[which.x], group = group[which.x])
            df$y <- NA
            for (i in levels(group)) {
                igroup <- which(df$group == i)
                j <- nrow(df[igroup, ])
                            if (j > 0) df[igroup, ]$y <- seq_len(j)
            }
                        stack.y[which.x] <- (df$y - 1) * ydist + y.min
        }
        stack.y
    }
}