R: legend with points and lines being different colors (for the same legend item)

Question

Using the legend() function is it possible to have the point and line be different colors? I feel like I'm missing something fairly obvious. The pt.bg option can change the background color, but I'm not seeing a pt.fg option

The arises in the case when you use the lines() and points() command separately with different colors and want the legend to represent what is plotted.

I thought it might be possible with the merge options, but I clearly don't quite understand what that is for.

Example:

plot( 0, type="n", xlim=c(0,5), ylim=c(0,5) ) A <- matrix( c( c(1,2,3,4), c(2,1,2,4)), ncol=2 ) B <- matrix( c( c(1,2,3,4), c(1,3,3,2)), ncol=2 ) lines( A, col="red" ) points( A, col="blue", pch=15 ) lines( B, col="green" ) points( B, col="purple", pch=17 )  legend( x="topleft",          legend=c("Red line, blue points","Green line, purple points"),         col=c("red","green"), lwd=1, lty=c(1,2),          pch=c(15,17) )  legend( x="bottomleft",          legend=c("Red line","blue points","Green line","purple points"),         col=c("red","blue","green","purple"), lwd=1, lty=c(1,NA,2,NA),         pch=c(NA,15,NA,17) )  legend( x="left",          legend=c("Red line, blue points","Green line, purple points"),         col=c("red","green"), lwd=1, lty=c(1,2), pch=c(15,17), merge=FALSE )  legend( x="bottomright",          legend=c("Red line","blue points","Green line","purple points"),          col=c("red","blue","green","purple"), lwd=1, lty=c(1,NA,2,NA),          pch=c(NA,15,NA,17), merge=FALSE )  legend( x="topright",          legend=c("Red line, blue points","Green line, purple points"),          col=c("red","blue","green","purple"), lwd=1, lty=c(1,2),          pch=c(15,17), merge=FALSE ) 

Solution

I hacked the legend() function to use two different color vectors:

LEGEND <- function (x, y = NULL, legend, fill = NULL,      col = par("col"), pt.col=col, line.col=col,     border = "black", lty, lwd, pch, angle = 45, density = NULL,     bty = "o", bg = par("bg"), box.lwd = par("lwd"), box.lty = par("lty"),     box.col = par("fg"), pt.bg = NA, cex = 1, pt.cex = cex, pt.lwd = lwd,     xjust = 0, yjust = 1, x.intersp = 1, y.intersp = 1, adj = c(0,         0.5), text.width = NULL, text.col = par("col"), text.font = NULL,     merge = do.lines && has.pch, trace = FALSE, plot = TRUE,     ncol = 1, horiz = FALSE, title = NULL, inset = 0, xpd, title.col = text.col,     title.adj = 0.5, seg.len = 2) {     if (missing(legend) && !missing(y) && (is.character(y) ||         is.expression(y))) {         legend <- y         y <- NULL     }     mfill <- !missing(fill) || !missing(density)     if (!missing(xpd)) {         op <- par("xpd")         on.exit(par(xpd = op))         par(xpd = xpd)     }     title <- as.graphicsAnnot(title)     if (length(title) > 1)         stop("invalid 'title'")     legend <- as.graphicsAnnot(legend)     n.leg <- if (is.call(legend))         1     else length(legend)     if (n.leg == 0)         stop("'legend' is of length 0")     auto <- if (is.character(x))         match.arg(x, c("bottomright", "bottom", "bottomleft",             "left", "topleft", "top", "topright", "right", "center"))     else NA     if (is.na(auto)) {         xy <- xy.coords(x, y)         x <- xy$x         y <- xy$y         nx <- length(x)         if (nx < 1 || nx > 2)             stop("invalid coordinate lengths")     }     else nx <- 0     xlog <- par("xlog")     ylog <- par("ylog")     rect2 <- function(left, top, dx, dy, density = NULL, angle,         ...) {         r <- left + dx         if (xlog) {             left <- 10^left             r <- 10^r         }         b <- top - dy         if (ylog) {             top <- 10^top             b <- 10^b         }         rect(left, top, r, b, angle = angle, density = density,             ...)     }     segments2 <- function(x1, y1, dx, dy, ...) {         x2 <- x1 + dx         if (xlog) {             x1 <- 10^x1             x2 <- 10^x2         }         y2 <- y1 + dy         if (ylog) {             y1 <- 10^y1             y2 <- 10^y2         }         segments(x1, y1, x2, y2, ...)     }     points2 <- function(x, y, ...) {         if (xlog)             x <- 10^x         if (ylog)             y <- 10^y         points(x, y, ...)     }     text2 <- function(x, y, ...) {         if (xlog)             x <- 10^x         if (ylog)             y <- 10^y         text(x, y, ...)     }     if (trace)         catn <- function(...) do.call("cat", c(lapply(list(...),             formatC), list("\n")))     cin <- par("cin")     Cex <- cex * par("cex")     if (is.null(text.width))         text.width <- max(abs(strwidth(legend, units = "user",             cex = cex, font = text.font)))     else if (!is.numeric(text.width) || text.width < 0)         stop("'text.width' must be numeric, >= 0")     xc <- Cex * xinch(cin[1L], warn.log = FALSE)     yc <- Cex * yinch(cin[2L], warn.log = FALSE)     if (xc < 0)         text.width <- -text.width     xchar <- xc     xextra <- 0     yextra <- yc * (y.intersp - 1)     ymax <- yc * max(1, strheight(legend, units = "user", cex = cex)/yc)     ychar <- yextra + ymax     if (trace)         catn("  xchar=", xchar, "; (yextra,ychar)=", c(yextra,             ychar))     if (mfill) {         xbox <- xc * 0.8         ybox <- yc * 0.5         dx.fill <- xbox     }     do.lines <- (!missing(lty) && (is.character(lty) || any(lty >         0))) || !missing(lwd)     n.legpercol <- if (horiz) {         if (ncol != 1)             warning(gettextf("horizontal specification overrides: Number of columns := %d",                 n.leg), domain = NA)         ncol <- n.leg         1     }     else ceiling(n.leg/ncol)     has.pch <- !missing(pch) && length(pch) > 0     if (do.lines) {         x.off <- if (merge)             -0.7         else 0     }     else if (merge)         warning("'merge = TRUE' has no effect when no line segments are drawn")     if (has.pch) {         if (is.character(pch) && !is.na(pch[1L]) && nchar(pch[1L],             type = "c") > 1) {             if (length(pch) > 1)                 warning("not using pch[2..] since pch[1L] has multiple chars")             np <- nchar(pch[1L], type = "c")             pch <- substr(rep.int(pch[1L], np), 1L:np, 1L:np)         }         if (!is.character(pch))             pch <- as.integer(pch)     }     if (is.na(auto)) {         if (xlog)             x <- log10(x)         if (ylog)             y <- log10(y)     }     if (nx == 2) {         x <- sort(x)         y <- sort(y)         left <- x[1L]         top <- y[2L]         w <- diff(x)         h <- diff(y)         w0 <- w/ncol         x <- mean(x)         y <- mean(y)         if (missing(xjust))             xjust <- 0.5         if (missing(yjust))             yjust <- 0.5     }     else {         h <- (n.legpercol + (!is.null(title))) * ychar + yc         w0 <- text.width + (x.intersp + 1) * xchar         if (mfill)             w0 <- w0 + dx.fill         if (do.lines)             w0 <- w0 + (seg.len + x.off) * xchar         w <- ncol * w0 + 0.5 * xchar         if (!is.null(title) && (abs(tw <- strwidth(title, units = "user",             cex = cex) + 0.5 * xchar)) > abs(w)) {             xextra <- (tw - w)/2             w <- tw         }         if (is.na(auto)) {             left <- x - xjust * w             top <- y + (1 - yjust) * h         }         else {             usr <- par("usr")             inset <- rep_len(inset, 2)             insetx <- inset[1L] * (usr[2L] - usr[1L])             left <- switch(auto, bottomright = , topright = ,                 right = usr[2L] - w - insetx, bottomleft = ,                 left = , topleft = usr[1L] + insetx, bottom = ,                 top = , center = (usr[1L] + usr[2L] - w)/2)             insety <- inset[2L] * (usr[4L] - usr[3L])             top <- switch(auto, bottomright = , bottom = , bottomleft = usr[3L] +                 h + insety, topleft = , top = , topright = usr[4L] -                 insety, left = , right = , center = (usr[3L] +                 usr[4L] + h)/2)         }     }     if (plot && bty != "n") {         if (trace)             catn("  rect2(", left, ",", top, ", w=", w, ", h=",                 h, ", ...)", sep = "")         rect2(left, top, dx = w, dy = h, col = bg, density = NULL,             lwd = box.lwd, lty = box.lty, border = box.col)     }     xt <- left + xchar + xextra + (w0 * rep.int(0:(ncol - 1),         rep.int(n.legpercol, ncol)))[1L:n.leg]     yt <- top - 0.5 * yextra - ymax - (rep.int(1L:n.legpercol,         ncol)[1L:n.leg] - 1 + (!is.null(title))) * ychar     if (mfill) {         if (plot) {             if (!is.null(fill))                 fill <- rep_len(fill, n.leg)             rect2(left = xt, top = yt + ybox/2, dx = xbox, dy = ybox,                 col = fill, density = density, angle = angle,                 border = border)         }         xt <- xt + dx.fill     }     if (plot && (has.pch || do.lines)) {         pt.COL <- rep_len(pt.col, n.leg)         line.COL <- rep_len(line.col, n.leg)     }     if (missing(lwd) || is.null(lwd))         lwd <- par("lwd")     if (do.lines) {         if (missing(lty) || is.null(lty))             lty <- 1         lty <- rep_len(lty, n.leg)         lwd <- rep_len(lwd, n.leg)         ok.l <- !is.na(lty) & (is.character(lty) | lty > 0) &             !is.na(lwd)         if (trace)             catn("  segments2(", xt[ok.l] + x.off * xchar, ",",                 yt[ok.l], ", dx=", seg.len * xchar, ", dy=0, ...)")         if (plot)             segments2(xt[ok.l] + x.off * xchar, yt[ok.l], dx = seg.len *                 xchar, dy = 0, lty = lty[ok.l], lwd = lwd[ok.l],                 col = line.COL[ok.l])         xt <- xt + (seg.len + x.off) * xchar     }     if (has.pch) {         pch <- rep_len(pch, n.leg)         pt.bg <- rep_len(pt.bg, n.leg)         pt.cex <- rep_len(pt.cex, n.leg)         pt.lwd <- rep_len(pt.lwd, n.leg)         ok <- !is.na(pch)         if (!is.character(pch)) {             ok <- ok & (pch >= 0 | pch <= -32)         }         else {             ok <- ok & nzchar(pch)         }         x1 <- (if (merge && do.lines)             xt - (seg.len/2) * xchar         else xt)[ok]         y1 <- yt[ok]         if (trace)             catn("  points2(", x1, ",", y1, ", pch=", pch[ok],                 ", ...)")         if (plot)             points2(x1, y1, pch = pch[ok], col = pt.COL[ok], cex = pt.cex[ok],                 bg = pt.bg[ok], lwd = pt.lwd[ok])     }     xt <- xt + x.intersp * xchar     if (plot) {         if (!is.null(title))             text2(left + w * title.adj, top - ymax, labels = title,                 adj = c(title.adj, 0), cex = cex, col = title.col)         text2(xt, yt, labels = legend, adj = adj, cex = cex,             col = text.col, font = text.font)     }     invisible(list(rect = list(w = w, h = h, left = left, top = top),         text = list(x = xt, y = yt))) } 

And used as follows:

LEGEND( x="bottomleft",          legend=c("Red line, blue points","Green line, purple points"),         col=c("red","green"),          lwd=1, lty=c(1,2), pch=c(15,17) )  LEGEND( x="bottomright",          legend=c("Red line, blue points","Green line, purple points"),         pt.col=c("blue","purple"), line.col=c("red","green"),         lwd=1, lty=c(1,2), pch=c(15,17) ) 

Answer 1

You can do this with 2 calls to legend, the 1st time plots the lines, then the second call plots over the top with invisible lines, but plots the points in the desired colors:

plot( 0, type="n", xlim=c(0,5), ylim=c(0,5) ) A <- matrix( c( c(1,2,3,4), c(2,1,2,4)), ncol=2 ) B <- matrix( c( c(1,2,3,4), c(1,3,3,2)), ncol=2 ) lines( A, col="red" ) points( A, col="blue", pch=15 ) lines( B, col="green" ) points( B, col="purple", pch=17 )  legend( x="topleft",          legend=c("Red line, blue points","Green line, purple points"),         col=c("red","green"), lwd=1, lty=c(1,2),          pch=c(NA,NA) )  legend( x="topleft",          legend=c("Red line, blue points","Green line, purple points"),         col=c("blue","purple"), lwd=1, lty=c(0,0),          pch=c(15,17) ) 

or for the second call to legend you can do something like this (so you don't have 2 copies of the text on top of each other):

legend( x="topleft",          legend=c("",""),         col=c("blue","purple"), lwd=1, lty=c(0,0),          pch=c(15,17), bty='n' ) 

Of course this only lines up properly working from the left. If you want the plot in one of the right corners then save the return value from the first call to legend and use it for placement in the second call.