r - how to extract dataframe name from a list using map - Stack Overflow

admin管理员组

文章数量:1410737

I tried to use 'map' to filter a list of dataset. how can I extract the name of dataframe, which is 'YYY' in my code.

library(dplyr)
library(purrr)

df1 <- data.frame(var1=seq(1:10), var2=seq(1:10), ID=1)
df2 <- data.frame(var2=seq(1:10), ID=2)
df3 <- data.frame(var3=seq(1:10), ID=3)
df_lst <- tibble::lst(df1, df2, df3)
codebook= data.frame(var.name = c("var1", "var2", "var3", "ID"),
                     df.name=c("df1", "df2", "df3", "ALL"))

try <- map(df_lst ~ {
data_sub <- codebook %>% filter(var.name %in% names(.x) & df.name %in% c( YYY, "ALL"))
.x %>% select(data_sub$var.name) 
})

I tried to use 'map' to filter a list of dataset. how can I extract the name of dataframe, which is 'YYY' in my code.

library(dplyr)
library(purrr)

df1 <- data.frame(var1=seq(1:10), var2=seq(1:10), ID=1)
df2 <- data.frame(var2=seq(1:10), ID=2)
df3 <- data.frame(var3=seq(1:10), ID=3)
df_lst <- tibble::lst(df1, df2, df3)
codebook= data.frame(var.name = c("var1", "var2", "var3", "ID"),
                     df.name=c("df1", "df2", "df3", "ALL"))

try <- map(df_lst ~ {
data_sub <- codebook %>% filter(var.name %in% names(.x) & df.name %in% c( YYY, "ALL"))
.x %>% select(data_sub$var.name) 
})

• r
• tidyverse
• purrr

Share Improve this question Follow edited Mar 23 at 17:53 zephryl 17.7k44 gold badges1616 silver badges3434 bronze badges asked Mar 23 at 15:10 StataqStataq 2,32399 silver badges1919 bronze badges

Add a comment  | 

2 Answers 2

Sorted by: Reset to default 1

purrr::imap() will pass the name of each element along with the element itself:

library(purrr)
library(dplyr)

imap(df_lst, \(df, nm) {
  data_sub <- codebook %>% 
    filter(var.name %in% names(df) & df.name %in% c(nm, "ALL"))
  df %>% select(data_sub$var.name) 
})

Note:

1. if you prefer formula-style lambdas (i.e., using ~ instead of \()), the names will be passed as .y.
2. the "manual" approach would be to iterate over names(df_list) instead of df_list, then access the dataframe within each iteration using df_list[[.x]].

Result:

$df1
   var1 ID
1     1  1
2     2  1
3     3  1
4     4  1
5     5  1
6     6  1
7     7  1
8     8  1
9     9  1
10   10  1

$df2
   var2 ID
1     1  2
2     2  2
3     3  2
4     4  2
5     5  2
6     6  2
7     7  2
8     8  2
9     9  2
10   10  2

$df3
   var3 ID
1     1  3
2     2  3
3     3  3
4     4  3
5     5  3
6     6  3
7     7  3
8     8  3
9     9  3
10   10  3

df_lst = mget(ls(pattern='^df\\d{1}$'))
lapply(names(df_lst), 
       \(d) df_lst[[d]][c(codebook$var.name[d==codebook$df.name], 'ID')])

ALL seems to be ID in any case, so it's hard-coded here. This fails if an element of c() is not in column names of df_lst[[d]].

本文标签： rhow to extract dataframe name from a list using mapStack Overflow