How to replace loop by apply function

Question

How to I do this using apply() functions ?

c <- c(df$Station, REF$Secteur, ETAT$Secteur) #three character type columns
for (i in c) {
  i <- toupper(i)
}

sapply(c,toupper)

This provides me with a list, but I would like the modifications to be applied to the original dataframes.

You maximise your chance of getting a useful answer if you provide a minimal reproducible example. [This post](https://stackoverflow.com/help/minimal-reproducible-example) may help. — Limey, Feb 09 '23 at 11:17
I don't believe it's possible to perform this action on three separate dataframes. If your context is much larger than three, it may be best to first bring all the columns into the same dataframe, use 'lapply' (like this https://stackoverflow.com/questions/18503177/r-apply-function-on-specific-dataframe-columns) then separate them again if necessary. — Bowhaven, Feb 09 '23 at 11:56

score 0 · Accepted Answer · answered Feb 09 '23 at 12:12

Here is a way with mapply, test data at the end.
Firs, put the data.frames in a list and the names of the column to be changed in a list or in a vector, below they are in a vector.

df_list <- list(df, REF, ETAT)
cols_vec <- c("Station", "Secteur", "Secteur")

mapply(\(x, col) toupper(x[[col]]), df_list, cols_vec, SIMPLIFY = FALSE)
#> [[1]]
#> [1] "A" "B" "C"
#> 
#> [[2]]
#> [1] "ABC" "DEF" "XYZ" "U"  
#> 
#> [[3]]
#> [1] "ABC" "DEF" "XYZ"

^{Created on 2023-02-09 with reprex v2.0.2}

Now, to assign these results back to the data in the list, change function a bit, make it return the df's.

df <- data.frame(x = 1:3, Station = letters[1:3])
REF <- data.frame(Secteur = c("Abc", "def", "xyz", "u"))
ETAT <- data.frame(Secteur = c("Abc", "def", "xyz"), x = 1:3, y = 4:6)
df_list <- list(df, REF, ETAT)
cols_vec <- c("Station", "Secteur", "Secteur")

mapply(\(x, col) {
  x[[col]] <-  toupper(x[[col]])
  x
}, df_list, cols_vec, SIMPLIFY = FALSE)
#> [[1]]
#>   x Station
#> 1 1       A
#> 2 2       B
#> 3 3       C
#> 
#> [[2]]
#>   Secteur
#> 1     ABC
#> 2     DEF
#> 3     XYZ
#> 4       U
#> 
#> [[3]]
#>   Secteur x y
#> 1     ABC 1 4
#> 2     DEF 2 5
#> 3     XYZ 3 6

^{Created on 2023-02-09 with reprex v2.0.2}

If you want the original data.frames to change, try the following.

df_list <- mget(c("df", "REF", "ETAT"), envir = .GlobalEnv)
df_list <- mapply(\(x, col) {
  x[[col]] <-  toupper(x[[col]])
  x
}, df_list, cols_vec, SIMPLIFY = FALSE)

list2env(df_list, envir = .GlobalEnv)
#> <environment: R_GlobalEnv>

df
#>   x Station
#> 1 1       A
#> 2 2       B
#> 3 3       C
REF
#>   Secteur
#> 1     ABC
#> 2     DEF
#> 3     XYZ
#> 4       U
ETAT
#>   Secteur x y
#> 1     ABC 1 4
#> 2     DEF 2 5
#> 3     XYZ 3 6

^{Created on 2023-02-09 with reprex v2.0.2}

Test data

df <- data.frame(x = 1:3, Station = letters[1:3])
REF <- data.frame(Secteur = c("Abc", "def", "xyz", "u"))
ETAT <- data.frame(Secteur = c("Abc", "def", "xyz"), x = 1:3, y = 4:6)
df_list <- list(df, REF, ETAT)
cols_vec <- c("Station", "Secteur", "Secteur")

^{Created on 2023-02-09 with reprex v2.0.2}

How to replace loop by apply function

1 Answers1

Test data