Prevent change to dataframe format in R-CodePudding

I have a dataframe that must have a specific layout. Is there a way for me to make R reject any command I attempt that would change the number or names of the columns?

It is easy to check the format of the data table manually, but I have found no way to make R do it for me automatically every time I execute a piece of code.

regards

CodePudding user response：

You mention the names and columns need to be the same, also realize that with data.table also names are updated by reference. See the example below.

foo <- data.table(
  x = letters[1:5],
  y = LETTERS[1:5]
)

colnames <- names(foo)

colnames
# [1] "x" "y"

setnames(foo, colnames, c("a", "b"))
foo[, z := "oops"]

colnames
# [1] "a" "b" "z"

identical(colnames, names(foo))
# [1] TRUE

To check that both the columns and names are unalterated (and in same order here) you can take right away a copy of the names. And after each code run, you can check the current names with the copied names.

foo <- data.table(
  x = letters[1:5],
  y = LETTERS[1:5]
)

colnames <- copy(names(foo))

setnames(foo, colnames, c("a", "b"))
foo[, z := "oops"]

identical(colnames, names(foo))
[1] FALSE

colnames
# [1] "x" "y"

names(foo)
# [1] "a" "b" "z"

CodePudding user response：

This doesn’t offer the level of foolproof safety I think you’re looking for (hard to know without more details), but you could define a function operator that yields modified functions that error if changes to columns are detected:

same_cols <- function(fn) {
  function(.data, ...) {
    out <- fn(.data, ...)
    stopifnot(identical(sort(names(.data)), sort(names(out))))
    out
  }
}

For example, you could create modified versions of dplyr functions:

library(dplyr)

my_mutate <- same_cols(mutate)
my_summarize <- same_cols(summarize)

which work as usual if columns are preserved:

mtcars %>%
  my_mutate(mpg = mpg / 2) %>%
  head()

                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
Mazda RX4         10.50   6  160 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag     10.50   6  160 110 3.90 2.875 17.02  0  1    4    4
Datsun 710        11.40   4  108  93 3.85 2.320 18.61  1  1    4    1
Hornet 4 Drive    10.70   6  258 110 3.08 3.215 19.44  1  0    3    1
Hornet Sportabout  9.35   8  360 175 3.15 3.440 17.02  0  0    3    2
Valiant            9.05   6  225 105 2.76 3.460 20.22  1  0    3    1

mtcars %>% 
  my_summarize(across(everything(), mean))

       mpg    cyl     disp       hp     drat      wt     qsec     vs      am
1 20.09062 6.1875 230.7219 146.6875 3.596563 3.21725 17.84875 0.4375 0.40625
    gear   carb
1 3.6875 2.8125

But error if changes to columns are made:

mtcars %>%
  my_mutate(mpg2 = mpg / 2)

# Error in my_mutate(., mpg2 = mpg/2) : 
#   identical(sort(names(.data)), sort(names(out))) is not TRUE

mtcars %>%
  my_summarize(mpg = mean(mpg))

# Error in my_summarize(., mpg = mean(mpg)) : 
#   identical(sort(names(.data)), sort(names(out))) is not TRUE

You could edit the function operator to include more specific tests and informative error messages.