"+"和"+"之间有什么区别?ggplot2中的运算符和“％"magrittr中的运算符? [英] What is the difference between the "+" operator in ggplot2 and the "%>%" operator in magrittr?

问题描述

ggplot2中的"+" 运算符与magrittr中的％>％" 运算符有什么区别?

What is the difference between the "+" operator in ggplot2 and the "%>%" operator in magrittr?

有人告诉我它们是相同的，但是如果考虑以下脚本.

I was told that they are the same, however if we consider the following script.

library(magrittr)
library(ggplot2)

# 1. This works
ggplot(data = mtcars, aes(x=wt, y = mpg)) + geom_point()

# 2. This works
ggplot(data = mtcars) + aes(x=wt, y = mpg) + geom_point()

# 3. This works
ggplot(data = mtcars) + aes(x=wt, y = mpg) %>% geom_point()

# 4. But this doesn't
ggplot(data = mtcars) %>% aes(x=wt, y = mpg) %>% geom_point()

推荐答案

管道与 ggplot2 的添加方式非常不同.管道运算符％>％所做的就是将左侧的结果作为右侧的函数的第一个参数.例如:

Piping is very different from ggplot2's addition. What the pipe operator, %>%, does is take the result of the left-hand side and put it as the first argument of the function on the right-hand side. For example:

1:10 %>% mean()
# [1] 5.5

完全等同于 mean(1:10).管道对于替换多重嵌套函数(例如

Is exactly equivalent to mean(1:10). The pipe is more useful to replace multiply nested functions, e.g.,

x = factor(2008:2012)
x_num = as.numeric(as.character(x))
# could be rewritten to read from left-to-right as
x_num = x %>% as.character() %>% as.numeric()

但是在 R中％>％是什么意思的所有解释都很好，，您应该通读还有更多示例.

but this is all explained nicely over at What does %>% mean in R?, you should read through that for a couple more examples.

利用这些知识，我们可以将您的管道示例重新编写为嵌套函数，并看到它们仍在执行相同的操作；但现在(希望如此)很明显为什么#4不起作用:

Using this knowledge, we can re-write your pipe examples as nested functions and see that they still do the same things; but now it (hopefully) is obvious why #4 doesn't work:

# 3. This is acceptable ggplot2 syntax
ggplot(data = mtcars) + geom_point(aes(x=wt, y = mpg))

# 4. This is not
geom_point(aes(ggplot(data = mtcars), x=wt, y = mpg))

---

ggplot2 包括用于 ggplot 对象的特殊"+" 方法，该方法用于在绘图中添加图层.我不知道，直到您问了这个问题，它也可以与 aes()函数一起使用，但显然也已定义好了.这些都是在 ggplot2 中专门定义的.在ggplot2中使用 + 早于管道，尽管用法相似，但功能却大不相同.

---

ggplot2 includes a special "+" method for ggplot objects, which it uses to add layers to plots. I didn't know until you asked your question that it also works with the aes() function, but apparently that's defined as well. These are all specially defined within ggplot2. The use of + in ggplot2 predates the pipe, and while the usage is similar, the functionality is quite different.

作为有趣的旁注，Hadley Wickham(ggplot2的创建者)说:

As an interesting side-note, Hadley Wickham (the creator of ggplot2) said that:

...如果我较早发现管道，就永远不会有ggplot2，因为您可以将ggplot图形编写为

...if I'd discovered the pipe earlier, there never would've been a ggplot2, because you could write ggplot graphics as

ggplot(mtcars, aes(wt, mpg)) %>%
  geom_point() %>%
  geom_smooth()

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