如何使用晶格将更新的线条颜色合并到R中的图形的图例中？

Question

Context and Question:

I want to add a legend to a lattice plot in R that shows the density of two groups. I've changed the default colours to black and gray. However, the legend has not updated the colours.

• How can I get the lattice plot to use my updated colours in the legend?
• How can I control the position of the legend (I'd like to be able to place it inside the plot area)?

Working example:

set.seed(4444)
x1 <- rep("Group A", 50)
x2 <- rep("Group B", 50)
y1 <- rnorm(50, 0, 2)
y2 <- rnorm(50, 1, 2)
dtf <- data.frame(x=c(x1, x2), y =c(y1, y2))

print(densityplot(~y, groups=x, data=dtf,
    pch=".",
    cex=2,
    col=c("black", "gray"),
    auto.key=TRUE,
    xlab="Y"))

Answer 1

The legend color is a well-known annoyance in lattice. It looks like it is difficult to correct, because Deepayan recommends simpleTheme as a solution. For positioning, see Josh's answer.

print(densityplot(~y, groups=x, data=dtf,
              pch=".",
              cex=2,
              par.settings=simpleTheme(col=c("gray","black")),
              auto.key=TRUE,
              xlab="Y"))

Answer 2

There might be a more elegant solution, but this works well enough. Notice that the corner= argument can be used to place the legend anywhere inside the plot.

densityplot(~y, groups = x, data = dtf,
    pch = ".",
    cex = 2,
    col = c("black", "gray"),
    par.settings = list(superpose.line = list(col=c("black", "grey"))),
    auto.key = list(corner = c(0.95, 0.95)),
    xlab = "Y")