估计 ggplot2 中图例占用的地块百分比

Question

我有一些 ggplot 功能，但我想给用户一个警告，以防他们滥用它。问题是这样的：如果有很多组并且组名很长，图例就会变得很大，占据整个情节：

但如果我要更改地块名称，我会得到：

我有的是：

ggplot / ggbuild 对象
图的尺寸window（默认为 480 x 320）但可以更改。

我想用这些来估计图例占用的总面积（这样如果图例大小/绘图大小的比率太大，我可以发出警告）。这是我用来创建图形的一些示例代码：

library(ggplot2)

# stolen from https://ryouready.wordpress.com/2008/12/18/generate-random-string-name/
MHmakeRandomString <- function(n=1, lenght=12) {
    randomString <- c(1:n)                  
    for (i in 1:n)
    {
        randomString[i] <- paste(sample(c(0:9, letters, LETTERS),
                                        lenght, replace=TRUE),
                                 collapse="")
    }
    return(randomString)
}

makeData <- function(k, useLongNames = FALSE) {

    x <- c(1, 100)
    X <- cbind(1, x)
    b <- matrix(rnorm(2*k), k, 2)

    y <- numeric(2*k)
    for (i in seq_len(k))
        y[1:2 + 2*(i-1)] <- X %*% b[i, ]

    df <- data.frame(x = c(1, n), y = y)

    if (useLongNames) {
        df$g <- factor(rep(MHmakeRandomString(k), each = 2))
    } else {
        df$g <- factor(rep(1:k, each = 2))
    }

    return(df)

}

# okayish plot
df <- makeData(50)
g0 <- ggplot(data = df, aes(x = x, y = y, group = g, color = g)) +
    geom_line() + 
    guides(color=guide_legend(nrow=5)) 

# unreadable plot    
df <- makeData(50, useLongNames = TRUE)
g1 <- ggplot(data = df, aes(x = x, y = y, group = g, color = g)) +
    geom_line() + 
    guides(color=guide_legend(nrow=5))

# to plot
# x11(width = 480, height = 320)
# print(g0)
# x11(width = 480, height = 320)
# print(g1)

我认为答案在 ggplotGrob() 中的某处。但是，我不熟悉 grobs（并且找不到明确的文档）并且被困在

gGrob0 <- ggplotGrob(g0)
gGrob1 <- ggplotGrob(g1)
gGrob0$grobs[[15]]$grobs[[1]]$grobs # all legend elements

convertWidth(grobWidth(gGrob0$grobs[[15]]), unitTo = "inches") # 4.5128 inches
convertWidth(grobWidth(gGrob1$grobs[[15]]), unitTo = "inches") # 12.419 inches
# but this is not correct:
# number of legend columns x legend width <= plot width
# 10 * 12.419 <= 480

这似乎给了我很多关于我感兴趣的东西的信息。我如何将这些信息转换成图例将占用的总宽度？非常感谢。

Answer 1

这是我的解决方案（灵感来自 m-dz 的评论）。对象 g0 和 g1 来自问题中的代码。

plotAndPrintRatio <- function(g, width, height) {

    gGrob <- ggplotGrob(g)
    tmpfile <- tempfile(pattern = "png")
    png(tmpfile, width = width, height = height) # it is necessary to open a device
    plot(g)
    legendSize <- as.numeric(convertWidth(grobWidth(gGrob$grobs[[15]]), unitTo = "inches"))
    plotSize <-   as.numeric(convertWidth(grobWidth(gGrob$grobs[[7]]), unitTo = "inches"))
    print(legendSize / plotSize) # the ratio of legend size to plot size
    dev.off()

    return(tmpfile)
}

# problem only in the first plot
f1 <- plotAndPrintRatio(g0, width = 480, height = 320) # 0.6769345
f2 <- plotAndPrintRatio(g1, width = 480, height = 320) # 1.887872 --> too big!

# larger window size fixes the problem
f3 <- plotAndPrintRatio(g0, width = 1200, height = 900) # 0.2707738
f4 <- plotAndPrintRatio(g1, width = 1200, height = 900) # 0.7551488
filesList <- list(f1, f2, f3, f4)

# to show the saved pngs:
dev.off() # might be needed to clean up the plotting window
grid::grid.raster(png::readPNG(f1))
grid::grid.raster(png::readPNG(f2))
grid::grid.raster(png::readPNG(f3))
grid::grid.raster(png::readPNG(f4))

# to remove the tempfiles created:
# lapply(filesList, file.remove)

估计 ggplot2 中图例占用的地块百分比

Estimate percentage of plot taken up by legend in ggplot2

r

ggplot2

grob

r-grid