ggplot2 和其他函数之间的加号 (R) [英] Plus sign between ggplot2 and other function (R)

问题描述

我正在尝试获取此示例:

I'm trying to get this example:

ggplot(mpg, aes(displ, hwy)) + geom_point()

ggplot(mpg, aes(displ, hwy)) + geom_point()

有人能解释一下这两个函数之间发生了什么吗?

Can somebody explain me what's going on here between these 2 functions?

ggplot2 会重载plus"运算符吗?总结这两个的结果是什么，它分配给什么?它是特定于 R 的功能还是特定于 ggplot2 的功能?它是一种管道吗?

Does ggplot2 overload "plus" operator? What is the result of summarizing these 2, and what is it assigned to? Is it R-specific feature, or ggplot2-specific? Is it kind of pipe?

推荐答案

@Richard Scriven 在评论中引用的函数定义定义在 plot-construction.r，这可能会使它更清楚.您需要查看源代码以确切了解这两个(未导出的)函数的作用(调用的 LHS 是 theme 还是 ggplot 对象)但是这些名字应该给你一个很好的主意.返回值是通过添加"e2修改的e1.

The function definition that @Richard Scriven refers to in comment is defined in plot-construction.r, which might make it clearer. You'll need to go through the source to see exactly what those two (unexported) functions do (whether the LHS of the call is a theme or a ggplot object) but the names should give you a pretty good idea. The return value is e1 modified by "adding" e2.

"+.gg" <- function(e1, e2) {
  # Get the name of what was passed in as e2, and pass along so that it
  # can be displayed in error messages
  e2name <- deparse(substitute(e2))

  if      (is.theme(e1))  add_theme(e1, e2, e2name)
  else if (is.ggplot(e1)) add_ggplot(e1, e2, e2name)
}

所以，是的，对于继承类 gg 的对象(所有 ggplot2 对象)，+ 是重载的.

So, yes, + is overloaded for objects inheriting class gg (all ggplot2 objects).

我认为管道"(@alistaire 的评论)是一个误导性的比喻；这非常符合标准 Ops 组通用的风格.

I think 'pipe' (@alistaire's comment) is a misleading analogy; this is very much in the style of the standard Ops group generic.

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