英文:
What are the differences and use cases of the five Magrittr Pipes %>%, %<>%, %$%, %!>% and %T>%?
问题
Magrittr 有以下不同的管道符号：
%>%管道符%<>%赋值管道符%$%曝露管道符%!>%急切管道符%T>%分叉管道符
它们的区别和用途是什么？
英文:
Magrittr has those different pipes:
%>%Pipe%<>%Assignment pipe%$%Exposition pipe%!>%Eager pipe%T>%Tee pipe
What are their differences and use cases?
答案1
得分: 4
%>% 管道
将一个对象传递到一个函数或调用表达式中。
library(magrittr)1:10 %>% head() # 基本用法#[1] 1 2 3 4 5 61:10 %>% head # 也可以工作#[1] 1 2 3 4 5 6#1:3 %>% approxfun(1:3, 4:6) #但在这种情况下需要空括号#Error in if (is.na(method)) stop("invalid interpolation method") :1:3 %>% approxfun(1:3, 4:6)()#[1] 4 5 61:10 %>% head(3) # 使用lhs作为第一个参数#[1] 1 2 3"Ceci n'est pas une pipe" %>% gsub("une", "un", .) # 使用点占位符#[1] "Ceci n'est pas un pipe"1:3 %>% paste0(LETTERS[.], 0) # 当点嵌套时，lhs仍然首先放置#[1] "1A0" "2B0" "3C0"1:3 %>% {paste0(LETTERS[.], 0)} # 这可以用{}来避免#[1] "A0" "B0" "C0"
另请参阅：使用magrittr的%>%管道时不带空括号的函数有什么缺点？。
%<>% 赋值管道
将一个对象传递到一个函数或调用表达式中，并使用结果更新lhs对象。
x <- -2:2x %<>% abs %>% sortx # 0 1 1 2 2
%$% 公开管道
将lhs中的名称暴露给rhs表达式。当函数没有内置的数据参数时，这很有用。
iris %$% cor(Sepal.Length, Sepal.Width)#[1] -0.1175698
另请参阅：我应该使用%$%而不是%>%吗？。
%!>% 急切管道
从左到右进行评估。而%>%是惰性的，只在需要时评估管道表达式，%!>%是急切的，在每个步骤中评估传递的输入。它也在相同的环境中评估。
0 %!>% (\(x) {cat(1); x}) %!>% (\(x) cat(2)) # 从左到右评估#120 %>% (\(x) {cat(1); x}) %>% (\(x) cat(2)) # 仅评估cat(2)，因为第一个结果从未使用#21 %!>% assign("a", .) # 工作a#[1] 10 %>% assign("a", .) # 由于有额外的环境，不起作用a#[1] 10 %>% assign("a", ., envir=parent.env(environment())) # 明确指定要在哪里评估a#[1] 0
%T>% 泄漏管道
将一个值传递到一个函数或调用表达式中，并返回原始值而不是结果。当表达式用于其副作用时，比如绘图或打印时，这很有用。
matrix(1:4, 2) %T>% plot %>% sum # sum得到与plot相同的数据#[1] 10
另请参阅：magrittr泄漏管%T>%等效。
英文:
%>% Pipe
Pipe an object forward into a function or call expression.
library(magrittr)1:10 %>% head() # Basic use#[1] 1 2 3 4 5 61:10 %>% head # Works also#[1] 1 2 3 4 5 6#1:3 %>% approxfun(1:3, 4:6) #But in this case empty parentheses are needed#Error in if (is.na(method)) stop("invalid interpolation method") :1:3 %>% approxfun(1:3, 4:6)()#[1] 4 5 61:10 %>% head(3) # Use with lhs as first argument#[1] 1 2 3"Ceci n'est pas une pipe" %>% gsub("une", "un", .) # Using the dot place-holder#[1] "Ceci n'est pas un pipe"1:3 %>% paste0(LETTERS[.], 0) # When dot is nested, lhs is still placed first#[1] "1A0" "2B0" "3C0"1:3 %>% {paste0(LETTERS[.], 0)} # This can be avoided with {}#[1] "A0" "B0" "C0"
%<>% Assignment pipe
Pipe an object forward into a function or call expression and update the lhs object with the resulting value.
x <- -2:2x %<>% abs %>% sortx # 0 1 1 2 2
%$% Exposition pipe
Expose the names in lhs to the rhs expression. This is useful when functions do not have a built-in data argument.
iris %$% cor(Sepal.Length, Sepal.Width)#[1] -0.1175698
See also: Should I use %$% instead of %>%?.
%!>% Eager pipe
Evaluate from left to right. Whereas %>% is lazy and only evaluates the piped expressions when needed, %!>% is eager and evaluates the piped input at each step. Also it evaluates in the same environment.
0 %!>% (\(x) {cat(1); x}) %!>% (\(x) cat(2)) # Evaluates from left to right#120 %>% (\(x) {cat(1); x}) %>% (\(x) cat(2)) # Evaluates only cat(2) as the first result is never used#21 %!>% assign("a", .) # Worka#[1] 10 %>% assign("a", .) # Does not work as there is an additional environmenta#[1] 10 %>% assign("a", ., envir=parent.env(environment())) # Give explicitly where to evaluatea#[1] 0
%T>% Tee pipe
Pipe a value forward into a function- or call expression and return the original value instead of the result. This is useful when an expression is used for its side-effect, say plotting or printing.
matrix(1:4, 2) %T>% plot %>% sum # sum gets the same data like plot#[1] 10
See also: magrittr tee pipe %T>% equivalent.
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