管道如何与purrr map（）函数和“。” （点）符号 [英] How do pipes work with purrr map() function and the "." (dot) symbol

问题描述

当从purrr使用管道和map（）函数时，我对数据和变量如何传递感到困惑。例如，这段代码可以像我期望的那样工作：

When using both pipes and the map() function from purrr, I am confused about how data and variables are passed along. For instance, this code works as I expect:

library(tidyverse)

cars %>% 
  select_if(is.numeric) %>% 
  map(~hist(.))

然而，当我使用ggplot进行类似的尝试时，它的表现方式很奇怪。

Yet, when I try something similar using ggplot, it behaves in a strange way.

cars %>% 
  select_if(is.numeric) %>% 
  map(~ggplot(cars, aes(.)) + geom_histogram())

我猜这是因为。在这种情况下是传递一个向量到aes（），它期望一个列名。无论哪种方式，我希望我可以使用管道和map（）将每个数字列传递给ggplot函数。

I'm guessing this is because the "." in this case is passing a vector to aes(), which is expecting a column name. Either way, I wish I could pass each numeric column to a ggplot function using pipes and map(). Thanks in advance!

推荐答案

cars %>% 
  select_if(is.numeric) %>% 
  map2(., names(.), 
       ~{ggplot(data_frame(var = .x), aes(var)) + 
           geom_histogram() + 
           labs(x = .y)                    })

还有一些额外的步骤。

• 使用 map2 而不是 map code>。第一个参数是你传递它的数据框，第二个参数是该数据框的名称的向量，所以它知道因为 ggplot 只适用于数据框，并且

• 这还允许您访问 .y 代词来命名图。



• Use map2 instead of map. The first argument is the dataframe you're passing it, and the second argument is a vector of the names of that dataframe, so it knows what to map over.
• You then need to explicitly enframe your data, since ggplot only works on dataframes and coercible objects.
• This also gives you access to the .y pronoun to name the plots.

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