使用 Purrr 映射多个数据帧并将这些修改后的数据帧作为输出 [英] Map with Purrr multiple dataframes and have those modified dataframes as the output

问题描述

我有一个关于 Purrr 包中的地图功能的问题.

I've got a question with the map function from the Purrr package.

• 我可以使用 map 成功地将数据框列表传递给函数
• 输出仍然是一个列表，这是我的问题；我需要将修改后的数据框作为 R 对象

以 mtcars 数据集为例:

As an example with the mtcars dataset:

#I create a second df
mtcars2 <- mtcars 

#change one variable just to distinguish them 
mtcars2$mpg <- mtcars2$mpg / 2

#create the list
dflist <- list(mtcars,mtcars2)

#then, a simple function example
my_fun <- function(x) 

{x <- x %>%

    summarise(`sum of mpg` = sum(mpg), 
              `sum of cyl` = sum(cyl)
    ) 
}

#then, using map, this works and prints the desired results
list_results <- map(dflist,my_fun)

但是，我需要将修改后的 mtcars 和 mtcars2 保存为 r 对象(数据帧).

But, I would need to have the modified mtcars and mtcars2 saved as r objects (dataframes).

• 我应该为我的函数添加某种保存"选项吗?
• 我应该使用 map_df 还是 dmap ?(我的试验没有成功)

提前，非常感谢你们！

推荐答案

这是一个尝试:

library(purrr)
library(tidyverse)

mtcars2 <- mtcars 
mtcars2$mpg <- mtcars2$mpg / 2
dflist <- list(mtcars,mtcars2)

要保存对象，需要为它们指定特定名称，并使用:

To save the objects one would need to give them specific names, and use:

assign("name", object, envir = .GlobalEnv)

这是实现这一目标的一种方法:

here is one way to achieve that:

my_fun <- function(x, list) {
  listi <- list[[x]]
  assign(paste0("object_from_function_", x), dflist[[x]], envir = .GlobalEnv)
  x <- listi %>%
    summarise(`sum of mpg` = sum(mpg), 
              `sum of cyl` = sum(cyl)
    )
  return(x)
}

my_fun 有两个参数 - seq_along(list) 生成特定名称和要处理的 list

my_fun has two arguments - seq_along(list) to generate specific names and the list that is to be processed

这会保存两个对象 object_from_function_1 和 object_from_function_2:

this saves two objects object_from_function_1 and object_from_function_2:

list_results <- map(seq_along(dflist), my_fun, dflist)

另一种方法是在地图函数之外使用 list2env 作为 akrun 建议

another approach would be to use list2env outside of the map function as akrun suggested

dflist <- list(mtcars,mtcars2)
names(dflist) <- c("mtcars","mtcars2")
list2env(dflist, envir = .GlobalEnv) #this will create two objects `mtcars` and `mtcars2`

并在创建对象后运行 map，就像您已经完成的那样.

and run map after you have created the objects as you have already done.

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