R 星图较小的 unit.key

Question

The following command will generate a star plot,

stars(mtcars[, 1:7], key.loc = c(14, 1.5), main = "Motor Trend Cars : full stars()")

how to make the unit key(bottom right corner) smaller or bigger?

Answer 1

If I understand properly, you want to increase the key polygon leaving the same size of the data polygons. Unfortunatelly, it is not possible. If we look at the source code of the stars() function, we will establish that the size of the both data and key polygons is controlled by the same argument len .

However, you may write you own modified stars() function making that possible. One way is to add an additional argument for the the key expansion, and define a separate length argument for the legend

stars2 <- function (x, key.exp = 1, .....)
{
    key_expansion <- key.exp
    len_legend <- key_expansion * len
    ...
}

Then the new length argument len_legend should be applied to draw the key instead of the old len argument. Thaht is, len should be replaced by len_legend inside the code which draws the key unit (the whole code chunk inside the if (!is.null(key.loc)) { .... } statement), like this:

   if (!is.null(key.loc)) {
        par(xpd = key.xpd)
        key.x <- len_legend * cos(angles) + key.loc[1L]
        key.y <- len_legend * sin(angles) + key.loc[2L]
       ...
   }

Let's check the results:

pdf("res_stars.pdf")
par(mfrow = c(1, 2))
    stars(mtcars[, 1:7], 
        key.loc = c(14, 1.5), 
        main = "Motor Trend Cars : full stars()",
        cex = 0.3)
    stars2(mtcars[, 1:7], 
        key_expansion = 1.3,
        key.loc = c(14, 1.5), 
        main = "Motor Trend Cars : full stars()",
        cex = 0.3)
dev.off()