使用dplyr的select引用变量名的位置 [英] Using dplyr's select where variable names are quoted

问题描述

通常，我想选择一个变量子集，其中子集是函数的结果。在这种简单的情况下，我首先获得所有与宽度特征有关的变量名

Often I'll want to select a subset of variables where the subset is the result of a function. In this simple case, I first get all the variable names which pertain to width characteristics

library(dplyr)
library(magrittr)

data(iris)

width.vars <- iris %>% 
                names %>% 
                extract(grep(".Width", .))

返回值：

>width.vars
 [1] "Sepal.Width" "Petal.Width"

能够使用这些返回值作为选择列的方式将很有用（而且我知道 contains（） 及其同级物存在，我想执行许多更复杂的子集，并且出于本示例的目的，使本示例变得微不足道。

It would be useful to be able to use these returns as a way to select columns (and while I'm aware that contains() and its siblings exist, there are plenty of more complicated subsets I would like to perform, and this example is made trivial for the purpose of this example.

如果我试图使用此功能作为选择列的方式，则会发生以下情况：

If I was to attempt to use this function as a way to select columns, the following happens:

iris %>% 
  select(Species,
         width.vars)

Error: All select() inputs must resolve to integer column positions.
The following do not:
*  width.vars

如何使用 dplyr :: select 带有以字符串形式存储的变量名向量？

How can I use dplyr::select with a vector of variable names stored as strings?

推荐答案

在 dplyr 内，大多数命令都有一个备用版本，其后缀为'_'，可以接受字符串作为输入。在这种情况下，请选择 select _ 。这些通常是在以编程方式使用 dplyr 时必须使用的。

Within dplyr, most commands have an alternate version that ends with a '_' that accept strings as input; in this case, select_. These are typically what you have to use when you are utilizing dplyr programmatically.

iris %>% select_(.dots=c("Species",width.vars))

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