使用 purrr::walk 从具有动态文件名的嵌套数据帧写入

Question

我正在使用 purrr::map 将函数应用于嵌套数据框，以获取新的数据框列表列。

现在我想使用同一行中的列值作为文件名的一部分将这些新数据帧中的每一个写入文件。

我不知道如何提取其他列值以便传递给文件名以写入文件。我相信purrr::walk 应该参与其中，但如何访问列变量和列表数据框内容的方式是问题所在。

下面的例子：

library(tibble) 
library(dplyr)
library(tidyr)  
library(purrr)

# Data
data("mtcars")
mtcars_nest <- mtcars %>% rownames_to_column() %>% rename(rowname_1 = rowname) %>% select(-mpg) %>% group_by(cyl) %>% nest()
mtcars_mpg <- mtcars %>% rownames_to_column() %>% rename(rowname_2 = rowname) %>% select(rowname_2, mpg)

# Function to apply to nested dataframe
join_df <- function(df_nest, df_other) {
  df_all <- inner_join(df_nest, df_other, by = c("rowname_1" = "rowname_2"))
  return(df_all)
}

# 1. Apply function to `$data` to get new dataframe list column and add an extra 'case' column for filename
mtcars_nest %>%
  mutate(case = c("first", "second", "third")) %>%
  mutate(new_mpg = map(data, ~ join_df(., mtcars_mpg)))

# 2. Now write `$new_mpg` to file with filename sources from $cyl and $case
# I think `walk` is the correct to use but how to pass the two row values into filename?

## Not real code##
# mtcars_nest %>%
#  walk(., function(x) {write.csv(., file = paste0(cyl, "_", case, ".csv")})

Answer 1

使用pwalk:

... %>%
select(cyl, case, new_mpg) %>%
pwalk(~ write.csv(..3, file = paste0(..1, '_', ..2, '.csv')))

---

在你的代码之后链接：

mtcars_nest %>%
    mutate(case = c("first", "second", "third")) %>%
    mutate(new_mpg = map(data, ~ join_df(., mtcars_mpg))) %>%
    select(cyl, case, new_mpg) %>%
    pwalk(~ write.csv(..3, file = paste0(..1, '_', ..2, '.csv')))