“磁力管”应用

Question

如何将对象输送到apply调用中的特定位置，这不是第一个输入？magrittr点占位符似乎不适用于此。

  dat <- 1:10 
  locs <- list(c(1, 2),
               c(3, 4),
               c(5, 6))
  
  foo <- function(x, y, z) {
    out <- mean(c(x[y], x[z]))
    return(out)
  }
  
  # works
  lapply(locs, function(z) foo(dat, z[1], z[2]))
  
  # none of these work 
  dat %>%
    lapply(locs, function(z) foo(., z[1], z[2]))
    
  dat %>%
    lapply(locs, function(z) foo((.), z[1], z[2]))
    
  dat %>%
    lapply(locs, function(z) {. %>% foo(z[1], z[2])})
    
  
  # New native pipe and placeholder also do not work
  dat |>
    lapply(locs, function(z) foo(_, z[1], z[2]))  

Answer 1

您可以像下面这样使用{}

>   dat %>%
+     {lapply(locs, function(z) foo(., z[1], z[2]))}
[[1]]
[1] 1.5

[[2]]
[1] 3.5

[[3]]
[1] 5.5