Non-redundant version of expand.grid

Sure! Here is an example of how to create a non-redundant version of the expand.grid function in R, along with explanations for each step.

nonredundant_expand.grid <- function(...) {
  args <- list(...)

  # Step 1: Get the number of arguments and their lengths
  num_args <- length(args)
  arg_lengths <- sapply(args, length)

  # Step 2: Create an empty matrix to store the combinations
  result <- matrix(nrow = prod(arg_lengths), ncol = num_args)

  # Step 3: Fill in the matrix with the combinations
  for (i in 1:num_args) {
    result[, i] <- rep.int(rep.int(args[[i]], each = prod(arg_lengths[-i])), times = prod(arg_lengths[-(1:i)]))
  }

  # Step 4: Return the matrix as a data frame
  as.data.frame(result)
}

Step 1: Get the number of arguments and their lengths In this step, we use the list function to convert the arguments passed to the function into a list. We then use the length function to get the number of arguments and the sapply function to get the lengths of each argument.

Step 2: Create an empty matrix to store the combinations In this step, we use the matrix function to create an empty matrix with the number of rows equal to the product of the lengths of all the arguments and the number of columns equal to the number of arguments.

Step 3: Fill in the matrix with the combinations In this step, we use a for loop to iterate over each argument. For each argument, we use the rep.int function to repeat the values of that argument, with the number of repetitions determined by the product of the lengths of all the other arguments. We then use the rep.int function again to repeat the resulting vector, with the number of repetitions determined by the product of the lengths of all the arguments after the current argument. We fill in the corresponding column of the matrix with the resulting vector.

Step 4: Return the matrix as a data frame In this step, we use the as.data.frame function to convert the matrix into a data frame and return it as the result of the function.

I hope this helps! Let me know if you have any further questions.