r - 使用 purrr :walk2 时找不到对象 .x

Question

我正在尝试在 purrr::walk2 处抛出一个函数，即:

library(stats19)
library(purrr)

walk2(.x = 2017, .y = "Accidents", .f = dl_stats19(year = .x, type = .y, data_dir = "./data", file_name = paste0("stats19_", .x, "_", .y), ask = FALSE))

# Error in dl_stats19(year = .x$years, type = types, data_dir = data_dir, : object '.x' not found

我不明白为什么 .x 没有在函数 dl_stats19()

中被提取

Answer 1

有几个可能的解决方案。第一种也是最简单的方法是在函数名称前包含波浪号，如下所示:

walk2(.x = 2017, 
      .y = "Accidents", 
      .f = ~ dl_stats19(year = .x, 
                        type = .y, 
                        data_dir = "./data", 
                        file_name = paste0("stats19_", .x, "_", .y), 
                        ask = FALSE))

您还可以使用匿名函数并按位置匹配参数，如下所示:

walk2(.x = 2017, 
      .y = "Accidents", 
      .f = function(a, b) dl_stats19(year = a, 
                                     type = b, 
                                     data_dir = "./data", 
                                     file_name = paste0("stats19_", a, "_", b), 
                                     ask = FALSE))