R-考虑到某些被调用的数据框可能不存在，如何合并/绑定多个数据框？

Question

I have to bind/merge dataframes in an iterative process in R. In occasions, some of the dataframes might not exist for reasons I will not explain here. I would like to know how I could bind dataframes even when calling some dataframe that does not exist. As an example, I have these dataframes:

df.R_H <- data.frame(A=c(0,4,5,6,7),
                  B=c(3,9,4,5,8),
                  C=c(1,2,4,2,6))

df.B_C <- data.frame(A=c(0,4,5,6,7),
                  B=c(3,9,4,5,8),
                  C=c(1,2,4,2,6))

df.G_H <- data.frame(A=c(0,4,5,6,7),
                  B=c(3,9,4,5,8),
                  C=c(1,2,4,2,6))

However, in my code I have this:

df5 <- rbind(df.R_H,df.B_C,df.G_H,df.R_C)
df5

How can I bind dataframes although df.R_C does not exist? I can not check individually which dataframes exists or not since I have hundreds of situations like this and I want to do it automatically even when some dataframe does not exist.

Answer 1

You can use mget() to get rbind() all data frames found in the environment. Alternatively for your example you could pass in x explicitly to mget() as paste0("df", 1:4) instead of ls() .

df1 <- data.frame(A=c(0,4,5,6,7),
                  B=c(3,9,4,5,8),
                  C=c(1,2,4,2,6))

df2 <- data.frame(A=c(0,4,5,6,7),
                  B=c(3,9,4,5,8),
                  C=c(1,2,4,2,6))

df3 <- data.frame(A=c(0,4,5,6,7),
                  B=c(3,9,4,5,8),
                  C=c(1,2,4,2,6))

df5 <- do.call(rbind, mget(ls(), mode = "list", ifnotfound = list(NULL)))
df5
#>       A B C
#> df1.1 0 3 1
#> df1.2 4 9 2
#> df1.3 5 4 4
#> df1.4 6 5 2
#> df1.5 7 8 6
#> df2.1 0 3 1
#> df2.2 4 9 2
#> df2.3 5 4 4
#> df2.4 6 5 2
#> df2.5 7 8 6
#> df3.1 0 3 1
#> df3.2 4 9 2
#> df3.3 5 4 4
#> df3.4 6 5 2
#> df3.5 7 8 6

If you have a crowded environment, which is likely, then you can utilize the pattern argument of ls() to ensure we only pull in relevant data frames through mget() . So if all your data frames start with df... , then you could use:

do.call(rbind, mget(ls(pattern = "^df*"), mode = "list", ifnotfound = list(NULL)))

Answer 2

Another possible solution:

library(tidyverse)

df.R_H <- data.frame(A=c(0,4,5,6,7),
                     B=c(3,9,4,5,8),
                     C=c(1,2,4,2,6))

df.B_C <- data.frame(A=c(0,4,5,6,7),
                     B=c(3,9,4,5,8),
                     C=c(1,2,4,2,6))

df.G_H <- data.frame(A=c(0,4,5,6,7),
                     B=c(3,9,4,5,8),
                     C=c(1,2,4,2,6))

map_dfr(list("df.R_H","df.B_C","df.G_H","df.R_C"), ~ if (exists(.x)) {get(.x)})

#>    A B C
#> 1  0 3 1
#> 2  4 9 2
#> 3  5 4 4
#> 4  6 5 2
#> 5  7 8 6
#> 6  0 3 1
#> 7  4 9 2
#> 8  5 4 4
#> 9  6 5 2
#> 10 7 8 6
#> 11 0 3 1
#> 12 4 9 2
#> 13 5 4 4
#> 14 6 5 2
#> 15 7 8 6