R lapply for list of lists to apply the same function to pre-defined columns

Question

I have a list of lists (2 df's) and want to use lapply to perform the same function for pre-defined columns in each df.

In particular I would like to use the winsorize function from the DescTools package. At the moment I know how to do this by specifying all individual columns within the function(x) command, which is, however, tedious if I have many columns (see example).

After applying the function, the entire list of lists (all columns) with the transformed variables should be returned. Ideally, the transformed variables are extended with "_w" (e.g. "price_w") or similar to indicate that these are the winsorized variables.

My data looks as follows, although I want to apply the function only to the pre-defined columns "price" and "quality".

id <- c(1, 5, 7, 9, 12)
country <- c("A", "A", "C", "E", "E")
price <- c(2.1, 4.6, 3.7, 2.9, 1.8)
quality <- c(3.1, 5.2, 3.3, 1.7, 0.9)
df1 <- cbind.data.frame(id, country, price, quality)

id <- c(2, 3, 4, 10, 14)
country <- c("F", "F", "A", "Z", "X")
price <- c(1.8, 5.2, 2.9, 4.6, 3.9)
quality <- c(4.3, 2.5, 6.9, 1.9, 0.8)
df2 <- cbind.data.frame(id, country, price, quality)

my.list <- list(df1, df2)

cols <- c("price", "quality")

This is what I have so far, which would only work for a small number of columns due to the necessary manual changes:

my.list <- lapply(my.list, function(x) {
  x$price_w <- DescTools::Winsorize(x$price, probs = c(.01, .99), na.rm = TRUE)
  x$quality_w <- DescTools::Winsorize(x$quality, probs = c(.01, .99), na.rm = TRUE)
  return(x)
})

Answer 1

We can use nested lapply to apply the function for multiple columns in each list.

lapply(my.list, function(x) {
  x[paste0(cols, '_w')] <- lapply(x[cols], DescTools::Winsorize)
  x
})

#[[1]]
#  id country price quality price_w quality_w
#1  1       A   2.1     3.1    2.10      3.10
#2  5       A   4.6     5.2    4.42      4.82
#3  7       C   3.7     3.3    3.70      3.30
#4  9       E   2.9     1.7    2.90      1.70
#5 12       E   1.8     0.9    1.86      1.06

#[[2]]
#  id country price quality price_w quality_w
#1  2       F   1.8     4.3    2.02      4.30
#2  3       F   5.2     2.5    5.08      2.50
#3  4       A   2.9     6.9    2.90      6.38
#4 10       Z   4.6     1.9    4.60      1.90
#5 14       X   3.9     0.8    3.90      1.02

Answer 2

One purrr and dplyr option could be:

map(.x = my.list,
    ~ .x %>%
     mutate(across(all_of(cols), 
                   list(w = ~ DescTools::Winsorize(., probs = c(.01, .99), na.rm = TRUE)))))

[[1]]
  id country price quality price_w quality_w
1  1       A   2.1     3.1   2.100     3.100
2  5       A   4.6     5.2   4.564     5.124
3  7       C   3.7     3.3   3.700     3.300
4  9       E   2.9     1.7   2.900     1.700
5 12       E   1.8     0.9   1.812     0.932

[[2]]
  id country price quality price_w quality_w
1  2       F   1.8     4.3   1.844     4.300
2  3       F   5.2     2.5   5.176     2.500
3  4       A   2.9     6.9   2.900     6.796
4 10       Z   4.6     1.9   4.600     1.900
5 14       X   3.9     0.8   3.900     0.844

Answer 3

here is a data.table solution

library( data.table )
library( DescTools )
#make df1 and df2 a data.table
my.list <- lapply( my.list, setDT )
#rund function on columns
lapply( my.list, function(x) {
  x[, paste0( (cols), "_w" ) := DescTools::Winsorize( .SD, 
                                                      probs = c(0.1, 0.9), 
                                                      na.rm = TRUE ), .SDcols = cols]
})

# 
# [[1]]
#    id country price quality price_w quality_w
# 1:  1       A   2.1     3.1     2.1      3.10
# 2:  5       A   4.6     5.2     4.6      4.66
# 3:  7       C   3.7     3.3     3.7      3.30
# 4:  9       E   2.9     1.7     2.9      1.70
# 5: 12       E   1.8     0.9     1.8      1.62
# 
# [[2]]
#    id country price quality price_w quality_w
# 1:  2       F   1.8     4.3     1.8      4.30
# 2:  3       F   5.2     2.5     5.2      2.50
# 3:  4       A   2.9     6.9     2.9      5.37
# 4: 10       Z   4.6     1.9     4.6      1.90
# 5: 14       X   3.9     0.8     3.9      1.70