expandGridIter With Repetitions

[drag05]

Would it possible to implement expandGridIter with repetition = TRUE so that the pool never diminishes?
Thank you!

[jwood000]

@drag05 Could you elaborate and provide an example with desired output?

Thanks

[drag05]

@jwood000 My question was in reference to permuteIter which has the formal repetition; I was wondering whether expandGridIter could receive a similar formal argument.

For example:

p = permuteIter(letters[1:4], 4, repetition = FALSE)
p@nextNIter(5)
     [,1] [,2] [,3] [,4]
[1,] "a"  "b"  "c"  "d" 
[2,] "a"  "b"  "d"  "c" 
[3,] "a"  "c"  "b"  "d" 
[4,] "a"  "c"  "d"  "b" 
[5,] "a"  "d"  "b"  "c" 

p = permuteIter(letters[1:4], 5, repetition = FALSE)
Error: m must be less than or equal to the length of v

p = permuteIter(letters[1:4], 5, repetition = TRUE)
p@nextNIter(5)
     [,1] [,2] [,3] [,4] [,5]
[1,] "a"  "a"  "a"  "a"  "a" 
[2,] "a"  "a"  "a"  "a"  "b" 
[3,] "a"  "a"  "a"  "a"  "c" 
[4,] "a"  "a"  "a"  "a"  "d" 
[5,] "a"  "a"  "a"  "b"  "a" 

Thank you!

[jwood000]

@drag05,

Thank you for your suggestion! I understand the concern about the repetition parameter in the context of the expandGrid function. However, I would like to clarify the rationale behind its exclusion.

In most functions in RcppAlgos, the repetition parameter is used when the source is a vector, allowing elements to be repeated up to a desired length (e.g., in combinations or permutations). When repetition = TRUE, elements can appear more than once in the result.

In the case of the comboGrid function, which is the only function where repetition is applied to a list of vectors, it controls whether or not the same element can appear in a particular result from different vectors in the list.

However, the expandGrid function generates the Cartesian product of vectors. Each entry in the grid is a combination of elements, where each element is chosen from one of the input vectors. The concept of repetition doesn't apply here because the "entries" in expandGrid are vectors themselves, not individual elements of a vector. Allowing repetition would not make sense in this context, as the Cartesian product inherently involves selecting one element from each input vector for every combination, without repeating the vectors themselves.

There is the idea of "repeating" the vectors themselves, with rep(list(v), n), but the user can easily supply this.

I hope this clears up the confusion.

[drag05]

@jwood000 No confusion! I had thought would be neat to implemented rep through formal argument(s). Thank you!