ggplot2：将变量移交给函数（非标准评估）[重复]

Question

我正在尝试编写一个函数，其中一个分组变量被移交给一个 ggplot2 表达式。

# sample data
df <- data.frame(x = rep(1:20, 5), y = rnorm(100), 
                 grp1 = c(rep("A", 20), rep("B", 20), rep("C", 20), rep("D", 20), rep("E", 20)),
                 grp2 = c(rep("X", 50), rep("Y", 50)),
                 stringsAsFactors = TRUE)

这行得通

g <- ggplot(df, aes(x, y, color = grp1)) +
  geom_line()

print(g)

这行不通

plot_this <- function(mydf, mygroup) {

  g <- ggplot(mydf, aes(x, y, color = mygroup)) +
    geom_line()
}

p <- plot_this(df, grp2)
print(p)
Error in FUN(X[[i]], ...) : object 'grp2' not found

这也不起作用（受 dplyr 启发）

plot_this <- function(mydf, mygroup) {

  mygroup <- enquo(mygroup)

  g <- ggplot(mydf, aes(x, y, color = (!! mygroup))) +
    geom_line()
}

p <- plot_this(df, grp2)
print(p)
Error in FUN(X[[i]], ...) : object 'grp2' not found

Answer 1

我错过了整洁的评估：

plot_this <- function(mydf, mygroup) {

  mygroup <- enquo(mygroup)

  g <- ggplot(mydf, aes(x, y, color = {{mygroup}})) +
    geom_line()
}

p <- plot_this(df, grp2)
print(p)