Pattern fill violin plots (vioplot package)

Question

Is there a way to fill violin plots with different patterns when using vioplot package to create plots in R?

I have figured out how to change color using col as shown below. But I don't even know how to begin with hatching in vioplot.

vioplot(random_value, at = 0.5, add = T, h = 0.04, col = 'lightsalmon4')

I have used density and angle but those don't help.

Answer 1

I am answering my own question just in case it might be useful to someone else later. It seems like vioplot package itself does not allow "hatching" or "texture" in the violin plot it creates. However, it seems like it can be achieved by making small changes to the default vioplot function to incorporate density and angle to the polygon it creates as the violin plots.

vioplot2 = function (x, ..., range = 1.5, h = NULL, ylim = NULL, names = NULL, 
    horizontal = FALSE, col = "magenta", border = "black", lty = 1, 
    lwd = 1, rectCol = "black", density = NA, angle = 45, colMed = "white", pchMed = 19, 
    at, add = FALSE, wex = 1, drawRect = TRUE) 
{
    datas <- list(x, ...)
    n <- length(datas)
    if (missing(at)) 
        at <- 1:n
    upper <- vector(mode = "numeric", length = n)
    lower <- vector(mode = "numeric", length = n)
    q1 <- vector(mode = "numeric", length = n)
    q3 <- vector(mode = "numeric", length = n)
    med <- vector(mode = "numeric", length = n)
    base <- vector(mode = "list", length = n)
    height <- vector(mode = "list", length = n)
    baserange <- c(Inf, -Inf)
    args <- list(display = "none")
    if (!(is.null(h))) 
        args <- c(args, h = h)
    for (i in 1:n) {
        data <- datas[[i]]
        data.min <- min(data)
        data.max <- max(data)
        q1[i] <- quantile(data, 0.25)
        q3[i] <- quantile(data, 0.75)
        med[i] <- median(data)
        iqd <- q3[i] - q1[i]
        upper[i] <- min(q3[i] + range * iqd, data.max)
        lower[i] <- max(q1[i] - range * iqd, data.min)
        est.xlim <- c(min(lower[i], data.min), max(upper[i], 
            data.max))
        smout <- do.call("sm.density", c(list(data, xlim = est.xlim), 
            args))
        hscale <- 0.4/max(smout$estimate) * wex
        base[[i]] <- smout$eval.points
        height[[i]] <- smout$estimate * hscale
        t <- range(base[[i]])
        baserange[1] <- min(baserange[1], t[1])
        baserange[2] <- max(baserange[2], t[2])
    }
    if (!add) {
        xlim <- if (n == 1) 
            at + c(-0.5, 0.5)
        else range(at) + min(diff(at))/2 * c(-1, 1)
        if (is.null(ylim)) {
            ylim <- baserange
        }
    }
    if (is.null(names)) {
        label <- 1:n
    }
    else {
        label <- names
    }
    boxwidth <- 0.05 * wex
    if (!add) 
        plot.new()
    if (!horizontal) {
        if (!add) {
            plot.window(xlim = xlim, ylim = ylim)
            axis(2)
            axis(1, at = at, label = label)
        }
        box()
        for (i in 1:n) {
            polygon(c(at[i] - height[[i]], rev(at[i] + height[[i]])), 
                c(base[[i]], rev(base[[i]])), col = col, density = density, angle = angle, border = border, 
                lty = lty, lwd = lwd)
            if (drawRect) {
                lines(at[c(i, i)], c(lower[i], upper[i]), lwd = lwd, 
                  lty = lty)
                rect(at[i] - boxwidth/2, q1[i], at[i] + boxwidth/2, 
                  q3[i], col = rectCol)
                points(at[i], med[i], pch = pchMed, col = colMed)
            }
        }
    }
    else {
        if (!add) {
            plot.window(xlim = ylim, ylim = xlim)
            axis(1)
            axis(2, at = at, label = label)
        }
        box()
        for (i in 1:n) {
            polygon(c(base[[i]], rev(base[[i]])), c(at[i] - height[[i]], 
                rev(at[i] + height[[i]])), col = col, density = density, angle = angle, border = border, 
                lty = lty, lwd = lwd)
            if (drawRect) {
                lines(c(lower[i], upper[i]), at[c(i, i)], lwd = lwd, 
                  lty = lty)
                rect(q1[i], at[i] - boxwidth/2, q3[i], at[i] + 
                  boxwidth/2, col = rectCol)
                points(med[i], at[i], pch = pchMed, col = colMed)
            }
        }
    }
    invisible(list(upper = upper, lower = lower, median = med, 
        q1 = q1, q3 = q3))
}

USAGE

set.seed(42)
x = rnorm(50,20,4)
vioplot2(x,density = 9, angle = 20)