How to make a functional list with the data.frames from the environment in R?-CodePudding

I want to join several data.frames in one. All the data.frames share an identical column.

There are different ways to merge several datasets and since I am using this approach Reduce(function(...) merge(..., all=TRUE), list( )) I need to get a list of the data.frames that I have in the environment. However, every time that I try to get a list of them, the features of being a data.frame disappear and they are only saved as a names.

These are my dataframes:

file_1 <- women
file_2 <- women
colnames(file_2) <- c("height_2", "weight_2")
file_3 <- women
colnames(file_3) <- c("height_3", "weight_3")
file_4 <- women
colnames(file_4) <- c("height_4", "weight_4")
file_5 <- women
colnames(file_5) <- c("height_5", "weight_5")

Since I want to merge them, I need to add the same column to all of them. With the first line of code, I make a list of the variables that I have in the environment (I only want the data.frames which start with the name "file")

list_files <- grep("file",names(.GlobalEnv),value=TRUE)

for (file in list_files){
  temp <- get(file)
  # We add the column 
  temp$ID <- "col"
  #we return the change in the file
  assign(file, temp)
}
rm(temp) #we don't need it anymore.

However, when I try to use list_files (which has the name of the data.frames) in order to merge them, I don't get a proper data.frame merged.

DF_complete <- Reduce(function(...) merge(..., all=TRUE), list(list_files))

> class(DF_complete)
[1] "character"

On the other hand, when I try this code (I write all the dataframes myself), I get the dataframe that I want.

DF_2 <- Reduce(function(...) merge(..., all=TRUE), list(file_1, file_2, file_3, file_4, file_5))

class(DF2)
[1] "data.frame"

I want to avoid writing all the data.frames. Right now I have 5 data.frames, but when I have more than 10.... it will be tough. For that reason, I want to find another way.

I saw this post and I have tried this, but they are not saved as data.frames.

list_df <- list(list_files)
> list_df
[[1]]
[1] "file_1" "file_2" "file_3" "file_4" "file_5"
class(list_df)
[1] "list"

Does anyone know how to do it?

Thanks very much in advance

CodePudding user response：

If we have multiple data.frames in the global environment that we want to merge, we can use mget and ls:

file_1 = data.frame(id = c(1,2), a = c(1,2))
file_2 = data.frame(id = c(1,2), b = c(3,4))
file_3 = data.frame(id = c(3,4), a = c(5,6))

Reduce(\(...) merge(..., all = T), mget(ls(pattern = "file")))
  id a  b
1  1 1  3
2  2 2  4
3  3 5 NA
4  4 6 NA