dplyr :: pull用裸或带引号的字符串作为参数？ [英] dplyr::pull with a bare or quoted string as an argument?

问题描述

基于阅读 dplyr：的文档：拉并检查示例，我的印象是 var 参数应为裸列名称。例如：

Based on reading the documentation of dplyr::pull and examining the examples, I am under the impression that the var argument should be a "bare column name". For example:

dplyr::pull(mtcars, cyl)
[1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4

但是，我刚刚意识到带引号的列名也可以使用：

However, I just realized that a quoted column name works too:

dplyr::pull(mtcars, "cyl")
[1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4

我只是好奇这两种样式之间是否存在差异。此外，使用第二种方法进行非交互用法（例如R程序包开发）有任何不利之处。

I am just curious as to whether there are any differences between these two styles. Moreover, are there any downsides of using the second option for say non-interactive usage (e.g. R package development).

我在这些方法中使用的是dplyr 0.7.4例子。

I have using version 0.7.4 of dplyr in these examples.

谢谢

推荐答案

pull 调用 select_var 使用准引用来计算或不计算参数，并最终从数据中返回列名。这样可以灵活地指定列，以支持交互和编程使用。

pull calls select_var which uses quasiquotation to evaluate or not the argument and eventually return a column name from the data. This allows the column to be specified in a flexible way that supports both interactive and programming use.

a <- "cyl"
select_var(names(mtcars), a)
[1] "cyl"
pull(mtcars,a)
 [1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4

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