ggplot2:将样本大小信息添加到x轴刻度标签

Question

此问题与 创建自定义geom以计算汇总统计信息并在*绘图区域外显示* (注意:所有函数都已简化;没有错误检查正确的对象类型,NA等)

在基础R中,很容易创建一个生成条带图的函数,其中样本大小在分组变量的每个级别下面指示:您可以使用以下mtext()函数添加样本大小信息:

stripchart_w_n_ver1 <- function(data, x.var, y.var) {
    x <- factor(data[, x.var])
    y <- data[, y.var]
# Need to call plot.default() instead of plot because 
# plot() produces boxplots when x is a factor.
    plot.default(x, y, xaxt = "n",  xlab = x.var, ylab = y.var)
    levels.x <- levels(x)
    x.ticks <- 1:length(levels(x))
    axis(1, at = x.ticks, labels = levels.x)
    n <- sapply(split(y, x), length)
    mtext(paste0("N=", n), side = 1, line = 2, at = x.ticks)
}

stripchart_w_n_ver1(mtcars, "cyl", "mpg")

或者您可以使用以下axis()函数将样本大小信息添加到x轴刻度标签:

stripchart_w_n_ver2 <- function(data, x.var, y.var) {
    x <- factor(data[, x.var])
    y <- data[, y.var]
# Need to set the second element of mgp to 1.5 
# to allow room for two lines for the x-axis tick labels.
    o.par <- par(mgp = c(3, 1.5, 0))
    on.exit(par(o.par))
# Need to call plot.default() instead of plot because 
# plot() produces boxplots when x is a factor.
    plot.default(x, y, xaxt = "n", xlab = x.var, ylab = y.var)
    n <- sapply(split(y, x), length)
    levels.x <- levels(x)
    axis(1, at = 1:length(levels.x), labels = paste0(levels.x, "\nN=", n))
}

stripchart_w_n_ver2(mtcars, "cyl", "mpg")

虽然这在基础R中是一项非常简单的任务,但它在ggplot2中非常复杂,因为很难获得用于生成绘图的数据,并且虽然有相当于axis()(例如scale_x_discrete,等等)的函数,但是没有相同的东西可以mtext()让你轻松地将文本放在边距内的指定坐标.

我尝试使用内置stat_summary()函数来计算样本大小(即fun.y = "length"),然后将该信息放在x轴刻度标签上,但据我所知,你无法提取样本大小然后以某种方式添加它们使用该功能到x轴刻度标签scale_x_discrete(),你必须告诉stat_summary()你想要它使用什么geom.你可以设置geom="text",但是你必须提供标签,关键是标签应该是样本大小的值,这stat_summary()是计算但你无法得到的(你还必须指定)您希望放置文本的位置,并且很难确定放置文本的位置,以便它直接位于x轴刻度标签下方.

插图"扩展ggplot2"(http://docs.ggplot2.org/dev/vignettes/extending-ggplot2.html)向您展示如何创建自己的stat函数,使您可以直接获取数据,但问题是你总是需要定义一个geom来配合你的stat函数(即,ggplot你认为你想在图中绘制这些信息,而不是在边距内); 据我所知,你不能在自定义统计函数中获取你计算的信息,不能在绘图区域中绘制任何东西,而是将信息传递给比例函数scale_x_discrete().这是我尝试这样做的方式; 我能做的最好的事情是将样本量信息放在每组的最小y值:

StatN <- ggproto("StatN", Stat,
    required_aes = c("x", "y"), 
    compute_group = function(data, scales) {
    y <- data$y
    y <- y[!is.na(y)]
    n <- length(y)
    data.frame(x = data$x[1], y = min(y), label = paste0("n=", n))
    }
)

stat_n <- function(mapping = NULL, data = NULL, geom = "text", 
    position = "identity", inherit.aes = TRUE, show.legend = NA, 
        na.rm = FALSE, ...) {
    ggplot2::layer(stat = StatN, mapping = mapping, data = data, geom = geom, 
        position = position, inherit.aes = inherit.aes, show.legend = show.legend, 
        params = list(na.rm = na.rm, ...))
}

ggplot(mtcars, aes(x = factor(cyl), y = mpg)) + geom_point() + stat_n()

我以为我通过简单地创建一个包装函数来解决问题ggplot:

ggstripchart <- function(data, x.name, y.name,  
    point.params = list(), 
    x.axis.params = list(labels = levels(x)), 
    y.axis.params = list(), ...) {
    if(!is.factor(data[, x.name]))
    data[, x.name] <- factor(data[, x.name])
    x <- data[, x.name]
    y <- data[, y.name]
    params <- list(...)
    point.params    <- modifyList(params, point.params)
    x.axis.params   <- modifyList(params, x.axis.params)
    y.axis.params   <- modifyList(params, y.axis.params)

    point <- do.call("geom_point", point.params)

    stripchart.list <- list(
        point, 
        theme(legend.position = "none")
    )

    n <- sapply(split(y, x), length)
    x.axis.params$labels <- paste0(x.axis.params$labels, "\nN=", n)
    x.axis <- do.call("scale_x_discrete", x.axis.params)
    y.axis <- do.call("scale_y_continuous", y.axis.params)
    stripchart.list <- c(stripchart.list, x.axis, y.axis)           

    ggplot(data = data, mapping = aes_string(x = x.name, y = y.name)) + stripchart.list
}


ggstripchart(mtcars, "cyl", "mpg")

但是,此功能在分面时无法正常工作.例如:

ggstripchart(mtcars, "cyl", "mpg") + facet_wrap(~am)

显示每个方面组合的两个面的样本大小.我必须在包装器功能中构建切面,这会破坏尝试使用所有ggplot必须提供的功能.

如果有人对这个问题有任何见解,我将不胜感激.非常感谢你的时间!

Answer 1

我已经更新了EnvStats 包以包含一个stat调用stat_n_text，它将在每个唯一的x值下方添加样本大小（唯一y值的数量）。查看帮助文件的更多信息和一系列例子。下面是一个简单的例子：stat_n_text

library(ggplot2)
library(EnvStats)

p <- ggplot(mtcars, 
  aes(x = factor(cyl), y = mpg, color = factor(cyl))) + 
  theme(legend.position = "none")

p + geom_point() + 
  stat_n_text() + 
  labs(x = "Number of Cylinders", y = "Miles per Gallon")

Answer 2

我的解决方案可能有点简单，但效果很好。

举一个由am刻面的示例，我首先使用paste和创建标签\n。

mtcars2 <- mtcars %>% 
  group_by(cyl, am) %>% mutate(n = n()) %>% 
  mutate(label = paste0(cyl,'\nN = ',n))

然后，我在ggplot代码中使用这些标签代替cyl

ggplot(mtcars2,
   aes(x = factor(label), y = mpg, color = factor(label))) + 
  geom_point() + 
  xlab('cyl') + 
  facet_wrap(~am, scales = 'free_x') +
  theme(legend.position = "none")

产生如下图所示的内容。

Answer 3

geom_text如果您关闭剪裁,则可以使用x轴标签下方的打印计数,但您可能需要调整放置位置.我在下面的代码中包含了一个"nudge"参数.此外,下面的方法适用于所有方面(如果有)是列方面的情况.

我意识到你最终想要的代码可以在一个新的geom中运行,但也许下面的例子可以适用于geom.

library(ggplot2)
library(dplyr)

pgg = function(dat, x, y, facet=NULL, nudge=0.17) {

  # Convert x-variable to a factor
  dat[,x] = as.factor(dat[,x])

  # Plot points
  p = ggplot(dat, aes_string(x, y)) +
    geom_point(position=position_jitter(w=0.3, h=0)) + theme_bw() 

  # Summarise data to get counts by x-variable and (if present) facet variables
  dots = lapply(c(facet, x), as.symbol)
  nn = dat %>% group_by_(.dots=dots) %>% tally

  # If there are facets, add them to the plot
  if (!is.null(facet)) {
    p = p + facet_grid(paste("~", paste(facet, collapse="+")))
  }

  # Add counts as text labels
  p = p + geom_text(data=nn, aes(label=paste0("N = ", nn$n)),
                    y=min(dat[,y]) - nudge*1.05*diff(range(dat[,y])), 
                    colour="grey20", size=3.5) +
    theme(axis.title.x=element_text(margin=unit(c(1.5,0,0,0),"lines")))

  # Turn off clipping and return plot
  p <- ggplot_gtable(ggplot_build(p))
  p$layout$clip[p$layout$name=="panel"] <- "off"
  grid.draw(p)

}

pgg(mtcars, "cyl", "mpg")
pgg(mtcars, "cyl", "mpg", facet=c("am","vs"))

另一种可能更灵活的选择是将计数添加到绘图面板的底部.例如:

pgg = function(dat, x, y, facet_r=NULL, facet_c=NULL) {

  # Convert x-variable to a factor
  dat[,x] = as.factor(dat[,x])

  # Plot points
  p = ggplot(dat, aes_string(x, y)) +
    geom_point(position=position_jitter(w=0.3, h=0)) + theme_bw() 

  # Summarise data to get counts by x-variable and (if present) facet variables
  dots = lapply(c(facet_r, facet_c, x), as.symbol)
  nn = dat %>% group_by_(.dots=dots) %>% tally

  # If there are facets, add them to the plot
  if (!is.null(facet_r) | !is.null(facet_c)) {

    facets = paste(ifelse(is.null(facet_r),".",facet_r), " ~ " , 
                   ifelse(is.null(facet_c),".",facet_c))

    p = p + facet_grid(facets)
  }

  # Add counts as text labels
  p + geom_text(data=nn, aes(label=paste0("N = ", nn$n)),
                y=min(dat[,y]) - 0.15*min(dat[,y]), colour="grey20", size=3) +
    scale_y_continuous(limits=range(dat[,y]) + c(-0.1*min(dat[,y]), 0.01*max(dat[,y])))
}

pgg(mtcars, "cyl", "mpg")
pgg(mtcars, "cyl", "mpg", facet_c="am")
pgg(mtcars, "cyl", "mpg", facet_c="am", facet_r="vs")