将向量传递给all()以测试相等性 [英] piping a vector into all() to test equality
问题描述
我正在尝试将向量传递到 all()
语句中,以检查所有元素是否都等于某个值。我想我需要使用博览会管道%$%
,因为 all()
没有内置数据论据。我的尝试导致错误:
I'm trying to pipe a vector into an all()
statement to check if all elements are equal to a certain value. I figure I need to use the exposition pipe %$%
since all()
does not have a built-in data argument. My attempt leads to an error:
library(tidyverse)
library(magrittr)
vec <- c("a", "b", "a")
vec %>%
keep(!grepl("b", .)) %$%
all(. == "a")
#> Error in eval(substitute(expr), data, enclos = parent.frame()): invalid 'envir' argument of type 'character'
如果我在 all()
之前断开管道并将输出分配给对象 p
,然后将 p
传递给 all()
作为第二个命令,它可以正常工作:
If I break the pipe before all()
and assign the output to an object p
, and then pass p
to all()
as a second command it works fine:
vec %>%
keep(!grepl("b", .)) -> p
all(p == "a")
#> [1] TRUE
我不明白为什么这样做有效,而我的第一次尝试却没有。我希望能够在单个管道中执行此操作,从而导致 TRUE
。
I don't understand why this works while my first attempt does not. I'd like to be able to do this in a single pipe that results in TRUE
.
如果 vec
而是 tibble
以下作品:
vec <- tibble(var = c("a", "b", "a"))
vec %>%
filter(!grepl("b", var)) %$%
all(.$var == "a")
#> [1] TRUE
这也不适合我的目的,我很适合自己
This doesn't suit my purposes as well, and I'd for my own understanding to know why my first attempt does not work.
推荐答案
管道的工作方式是它占据了管道的左侧。管道运算符,并将其作为第一个参数传递给右侧函数。因此,在这种情况下,由于需要将data参数修改为 all
,因此需要停止管道将LHS传递给RHS。我们可以使用 {}
来实现。
The way pipe works is it takes the left-hand side of the pipe operator and passes it as a first argument to the right hand side function. So here, in this case as we need to modify the data argument to all
, we need to stop pipe from passing the LHS to the RHS. We can do that by using {}
.
library(magrittr)
vec %>% purrr::keep(!grepl("b", .)) %>% {all(. == 'a')}
#[1] TRUE
在 vec
中,让我们检查所有元素是否都是 a
或 b
。我们可以在这里使用%in%
。
In vec
, let's check if all the elements are either "a"
or "b
". We can use %in%
here.
vec <- c("a", "b", "a")
不带管道的普通版本为:
Plain version without pipes would be :
all(vec %in% c('a', 'b'))
#[1] TRUE
如果使用管道,则尝试
vec %>% all(. %in% c('a', 'b'))
我们得到
#[1] NA
警告消息:
总共(。,。%in%c( a, b)):
类型为'character'的强制参数为逻辑
Warning message: In all(., . %in% c("a", "b")) : coercing argument of type 'character' to logical
这里发生了什么
all(vec, vec %in% c('a', 'b'))
#[1] NA
警告消息:
总计(vec,vec%in%c( a, b)):
强制类型为'character'的参数'到逻辑
Warning message: In all(vec, vec %in% c("a", "b")) : coercing argument of type 'character' to logical
会返回相同的消息。
为避免这种情况,我们使用 {}
To avoid this we use {}
vec %>% {all(. %in% c('a', 'b'))}
#[1] TRUE
这给了我们预期的答案。
which gives us the expected answer.
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