Apply self-defined function on list of data frames in R

Question

This is a follow-up to a previous question of mine: Code in R to conditionally subtract columns in data frames

I now want to apply the given solution to my previous problem

cols <- grep('^\\d+$', names(df), value = TRUE)
new_cols <- paste0(cols, '_corrected')
df[new_cols] <- df[cols] - df[paste0('Background_', cols)]
df[c("Wavelength", new_cols)]

to every data frame in a list. I import all sheets of an excel file so that every sheet becomes one data frame in a list using this code (courtesy of Read all worksheets in an Excel workbook into an R list with data.frames 's top answer):

read_excel_allsheets <- function(filename, tibble = FALSE) {
  sheets <- readxl::excel_sheets(filename)
  x <- lapply(sheets, function(X) readxl::read_excel(filename, sheet = X))
  if(!tibble) x <- lapply(x, as.data.frame)
  names(x) <- sheets
  x
}

mysheets <- read_excel_allsheets(file.choose())

How do I apply the first code box to my data frame list?

I want to get from something like this:

df_1 <- structure(list(Wavelength = 300:301, Background_1 = c(5L, 3L), 
                     `1` = c(11L, 12L), Background_2 = c(4L, 5L), `2` = c(12L, 10L)), 
                class = "data.frame", row.names = c(NA, -2L))

df_2 <- structure(list(Wavelength = 300:301, Background_1 = c(6L, 4L),
                     `1` = c(10L, 13L), Background_2 = c(5L, 6L), `2` = c(11L, 11L),
                     Background_3 = c(4L, 6L), `3` = c(13L, 13L)),
                class = "data.frame", row.names = c(NA, -2L))

df_list <- list(df_1, df_2)

To something like this:

df_1_corrected <- structure(list(Wavelength = 300:301, `1_corrected` = c(6L, 9L),
                                 `2_corrected` = c(8L, 5L)),
                class = "data.frame", row.names = c(NA, -2L))

df_2_corrected <- structure(list(Wavelength =300:301, `1_corrected` = c(4L, 9L),
                                 `2_corrected` = c(6L, 5L),
                                 `3_corrected` = c(9L, 7L)),
                class = "data.frame", row.names = c(NA, -2L))

df_corrected_list <- list(df_1_corrected, df_2_corrected)

actual data excerpt

Wavelength Background 1        1 Background 2       2 Background 3         3
       300     273290.0 337670.0     276740.0  397530     288500.0  367480.0
       301     299126.7 375143.3     299273.3  432250     310313.3  394796.7

I have read the lapply function would be used for this but i have never used it before, as I am quite the beginner in R. Help is much appreciated!

Answer 1

You can put the code in a function and apply it for each dataframe in list using lapply :

subtract_values <- function(df) {
  cols <- grep('^\\d+$', names(df), value = TRUE)
  new_cols <- paste0(cols, '_corrected')
  df[new_cols] <- df[cols] - df[paste0('Background ', cols)]
  df[c("Wavelength", new_cols)]
}

lapply(df_list, subtract_values)

#[[1]]
#  Wavelength 1_corrected 2_corrected
#1        300           6           8
#2        301           9           5

#[[2]]
#  Wavelength 1_corrected 2_corrected 3_corrected
#1        300           4           6           9
#2        301           9           5           7