在R中的另一个函数中使用ggplot（）

Question

我正在尝试使用ggplot2库编写一个简单的绘图函数。但是调用ggplot找不到函数参数。

考虑一个data.frame调用means，它存储了两个要绘制的条件和两个平均值（条件将出现在X轴上，均值出现在Y轴上）。

library(ggplot2)

m <- c(13.8, 14.8)

cond <- c(1, 2)

means <- data.frame(means=m, condition=cond)

means

# The output should be:

#     means    condition

#   1 13.8     1

#   2 14.8     2

testplot <- function(meansdf)

{

  p <- ggplot(meansdf, aes(fill=meansdf$condition, y=meansdf$means, x = meansdf$condition))

  p + geom_bar(position="dodge", stat="identity")

}

testplot(means)

# This will output the following error:

# Error in eval(expr, envir, enclos) : object 'meansdf' not found

所以似乎ggplot正在调用eval，找不到参数meansdf。有谁知道我如何成功地将函数参数传递给ggplot？

（注意：是的，我可以直接调用ggplot函数，但是最后我希望使我的plot函数做更复杂的事情！:)）

Answer 1

正如Joris和Chase已经正确回答的那样，标准的最佳实践是简单地省略meansdf$零件并直接引用数据框列。testplot <- function(meansdf){&nbsp; p <- ggplot(meansdf,&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; aes(fill = condition,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; y = means,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; x = condition))&nbsp; p + geom_bar(position = "dodge", stat = "identity")}之所以可行，是因为aes在全局环境中或在传递给的数据帧中寻找引用的变量ggplot。这也是为什么你的示例代码-使用meansdf$condition等-不工作：meansdf在全球环境既不可用，也不是可以传递到数据帧里面ggplot，这是meansdf本身。在全局环境中而不是在调用环境中寻找变量的事实实际上是ggplot2中的一个已知错误，Hadley目前认为该错误不可修复。如果希望使用局部变量（例如scale）来影响用于绘图的数据，则会导致问题：testplot <- function(meansdf){&nbsp; scale <- 0.5&nbsp; p <- ggplot(meansdf,&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; aes(fill = condition,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; y = means * scale,&nbsp; &nbsp;# does not work, since scale is not found&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; x = condition))&nbsp; p + geom_bar(position = "dodge", stat = "identity")}Winston Chang在引用的GitHub问题中提供了一种很好的解决方法：environment在调用时，将参数显式设置为当前环境ggplot。上面的示例如下所示：testplot <- function(meansdf){&nbsp; scale <- 0.5&nbsp; p <- ggplot(meansdf,&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; aes(fill = condition,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; y = means * scale,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; x = condition),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; environment = environment())&nbsp; &nbsp;# This is the only line changed / added&nbsp; p + geom_bar(position = "dodge", stat = "identity")}## Now, the following workstestplot(means)

Answer 2

这是一个简单的技巧，我在函数环境（第二行）中经常使用它来定义变量：FUN <- function(fun.data, fun.y) {&nbsp; &nbsp; fun.data$fun.y <- fun.data[, fun.y]&nbsp; &nbsp; ggplot(fun.data, aes(x, fun.y)) +&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; geom_point() +&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; scale_y_continuous(fun.y)&nbsp; &nbsp;&nbsp;}datas <- data.frame(x = rnorm(100, 0, 1),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; y = x + rnorm(100, 2, 2),&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; z = x + rnorm(100, 5, 10))FUN(datas, "y")FUN(datas, "z")请注意，当使用不同的变量或数据集时，y轴标签也会如何变化。