How to select specific columns across multiple dataframes in R and then bind them into one data.frame?

Question

I am trying to select or subset multiple data frames with different number of columns. They all contain the same columns of interest, so I am trying to make them all contain the same columns so I can then append into one data frame. I am trying to be as elegant and efficient as possible, but my codes does not seem to be working. This is what I tried to do:

Suppose I have the following data frames:

df1 <- matrix(1:12, 3,4, dimnames = list(NULL, LETTERS[1:4]))
df2 <- matrix(12:26, 3, 5, dimnames = list(NULL, LETTERS[1:5]))

df1 <- as.data.frame(df1)
df2 <- as.data.frame(df2)

I tried to subset both data frames creating a function and then using lapply. Suppose I only want to keep columns A, C, and D:

select_function <- function(x){
  dplyr::select(`A`,`C`,`D`)
}

list <- list(df1, df2)

df.list <- lapply(list, function(x) select_function)

I then tried to append the list into one data frame:

new.df <- do.call(rbind, df.list)

Codes are not working. I think the line with lapply is not correct, not sure what is being generated in df.list. I hope I could communicate what I tried to do. Please let me know alternative ways to achieve this.

SamR · Accepted Answer · 2024-07-16 16:57:02Z

1

You are not passing your data to your function. It should look like:

select_cols <- function(df) {
    df |>
        dplyr::select(A, C, D)
}

Then you can just do:

lapply(l, select_cols)
# [[1]]
#   A C  D
# 1 1 7 10
# 2 2 8 11
# 3 3 9 12

# [[2]]
#    A  C  D
# 1 12 18 21
# 2 13 19 22
# 3 14 20 23

Or alternatively, in base R:

cols <- c("A", "C", "D")
lapply(l, \(df) df[cols])
# [[1]]
#   A C  D
# 1 1 7 10
# 2 2 8 11
# 3 3 9 12

# [[2]]
#    A  C  D
# 1 12 18 21
# 2 13 19 22
# 3 14 20 23

answered Jul 16, 2024 at 16:57

SamR

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Comments

LMc · Accepted Answer · 2024-07-16 16:59:24Z

1

This will row bind your data frames and align like columns. Then you can simply select those like columns after the fact.

library(dplyr) 

bind_rows(df1, df2) |> 
  select(A, C, D)
#    A  C  D
# 1  1  7 10
# 2  2  8 11
# 3  3  9 12
# 4 12 18 21
# 5 13 19 22
# 6 14 20 23

answered Jul 16, 2024 at 16:59

LMc

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1 Comment

Victor Shin Over a year ago

oh, it works too! And with fewer lines. Thank you LMc!

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