dplyr的工作间隔如何？ [英] How does dplyr’s between work?

问题描述

我已经阅读了文档，并尝试对其进行谷歌搜索；这应该是一件简单的事情，但似乎对我而言不是；因此，我大胆地问一下，是否有人可以向我解释dplyr的 between（）的工作原理。

I’ve read the documentation and I’ve tried googling it; it should be a simple thing, but it would seem it’s not to me; so I boldly go forth and ask if someone here could explain me how dplyr’s between() works.

# Explanation documentation
between(x, left, right)

x            A numeric vector of values
left, right: Boundary values

我知道向量是一维数组，所以我想 c（1：7） 是向量，对吗？我尝试使用文档中提供的示例作为模板来搜索7月至9月的航班，但是以下内容仅返回错误：

I understand a vector is a one-dimensional array, so I suppose c(1:7) is a vector, right? I tried using the example provided in the documentation as a template to search for flights july–september, but the following just returns an error:

# Example from documentation cont’d
x <- rnorm(1e2)
x[between(x, -1, 1)]

# Loading the library
library(nycflights13)

# Execute my hopeless attempt at between()
flights[between(month, 7, 9)]

# Output and error message
> flights[between(month, 7, 9)]
Error in between(month, 7, 9) : object 'month' not found

我真是个愚蠢的人，但对此有任何帮助将不胜感激。我也很抱歉没有提出明确的问题；可能会得到赞赏，我真的不知道该怎么说，而是说我不明白。

I feel really daft asking this, but any help in understanding this will be greatly appreciated. I would also apologise for not asking a well-defined question; as is probably appreciated, I really don’t know how to phrase it other than ‘I don’t get it’.

推荐答案

之间没什么特别的，R中的任何其他函数都会导致相同的问题。您的困惑源于dplyr具有许多功能，这些功能使您可以像对待普通变量一样处理data.frame列名；例如：

between is nothing special — any other function in R would have led to the same problem. Your confusion stems from the fact that dplyr has a lot of functions that allow you to work on data.frame column names as if they were normal variables; for instance:

filter(flights, month > 9)

但是， 之间不是这些功能之一。如上所述，这只是正常功能。因此，如果要使用它，则需要以常规方式提供参数。例如：

However, between is not one of these functions. As mentioned, it’s simply a normal function. So if you want to use it, you need to provide arguments in the conventional way; for instance:

between(flights$month, 7, 9)

这将返回逻辑向量，您现在可以使用它来索引您的数据。

This will return a logical vector, and you can now use it to index your data.frame:

flights[between(flights$month, 7, 9), ]

或更像是dplyr：

flights %>% filter(between(month, 7, 9))

请注意，我们现在在此处使用非标准评估。但是评估是由过滤器执行的，而不是由之间的$code>执行的。使用标准评估调用之间的（通过过滤器）。

Note that here we now use non-standard evaluation. But the evaluation is performed by filter, not by between. between is called (by filter) using standard evaluation.

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