R：ggplot2，如何在面板图的每个面板上注释汇总统计数据

Question

如何使用 R 中的 ggplot2 在以下绘图的每个面板中添加标准偏差的文本注释（例如 sd = sd_value）？

library(datasets)
data(mtcars)
ggplot(data = mtcars, aes(x = hp)) + 
        geom_dotplot(binwidth = 1) + 
        geom_density() + 
        facet_grid(. ~ cyl) + 
        theme_bw()

我想要 post 情节的图像，但我没有足够的代表。

我认为 "geom_text" 或 "annotate" 可能有用，但我不确定如何使用。

Answer 1

如果您想在每个方面改变文本标签，您将需要使用 geom_text。如果你希望相同的文本出现在每个方面，你可以使用 annotate.

p <- ggplot(data = mtcars, aes(x = hp)) + 
  geom_dotplot(binwidth = 1) + 
  geom_density() + 
  facet_grid(. ~ cyl)

mylabels <- data.frame(cyl = c(4, 6, 8), 
                       label = c("first label", "seond label different", "and another"))

p + geom_text(x = 200, y = 0.75, aes(label = label), data = my labels)

### compare that to this way with annotate

p + annotate("text", x = 200, y = 0.75, label = "same label everywhere")

现在，如果在这个例子中你真的想要 cyl 的标准差，我可能会先使用 dplyr 进行计算，然后像这样用 geom_text 完成计算:

library(ggplot2)
library(dplyr)

df.sd.hp <- mtcars %>%
  group_by(cyl) %>%
  summarise(hp.sd = round(sd(hp), 2))

ggplot(data = mtcars, aes(x = hp)) + 
  geom_dotplot(binwidth = 1) + 
  geom_density() + 
  facet_grid(. ~ cyl) +
  geom_text(x = 200, y = 0.75, 
            aes(label = paste0("SD: ", hp.sd)), 
            data = df.sd.hp)

Answer 2

我更喜欢当统计信息出现在构面标签本身中时的图形外观。我制作了以下脚本，它允许选择显示 标准偏差 、mean 或 count。本质上，它计算汇总统计信息，然后将其与名称合并，以便您具有格式 CATEGORY (SUMMARY STAT = VALUE).

   #' Function will update the name with the statistic of your choice
AddNameStat <- function(df, category, count_col, stat = c("sd","mean","count"), dp= 0){

  # Create temporary data frame for analysis
  temp <- data.frame(ref = df[[category]], comp = df[[count_col]])

  # Aggregate the variables and calculate statistics
  agg_stats <- plyr::ddply(temp, .(ref), summarize,
                           sd = sd(comp),
                           mean = mean(comp),
                           count = length(comp))

  # Dictionary used to replace stat name with correct symbol for plot
  labelName <- mapvalues(stat, from=c("sd","mean","count"), to=c("\u03C3", "x", "n"))

  # Updates the name based on the selected variable
  agg_stats$join <- paste0(agg_stats$ref, " \n (", labelName," = ",
                           round(agg_stats[[stat]], dp), ")")

  # Map the names
  name_map <- setNames(agg_stats$join, as.factor(agg_stats$ref))
  return(name_map[as.character(df[[category]])])
}

将此脚本用于您的原始问题：

library(datasets)
data(mtcars)

# Update the variable name
mtcars$cyl  <- AddNameStat(mtcars, "cyl", "hp", stat = "sd")

ggplot(data = mtcars, aes(x = hp)) + 
  geom_dotplot(binwidth = 1) + 
  geom_density() + 
  facet_grid(. ~ cyl) + 
  theme_bw()

脚本应该很容易更改以包含其他摘要统计信息。我也确信它可以部分重写，使它更干净一些！

R：ggplot2，如何在面板图的每个面板上注释汇总统计数据

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