Allow assignment of size 1 with Subsetter

[fplazaonate]

R allows singleton vectors to be assigned to vectors subsets with more than one element.

Here is an example:

> v1=c(1,2,3)
> v2=c(4)
> v1[v1<4]=v2
> v1
[1] 4 4 4

This feature is currently not available in Rcpp as previously discussed in #345

Code:

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
IntegerVector test()
{
  IntegerVector v1 = IntegerVector::create(1,2,3);
  IntegerVector v2 = IntegerVector::create(4);
  v1[v1<4] = v2;

  return v1;
}

/*** R
test()
*/

Result:

test()
Error in eval(expr, envir, enclos) : index error

This PR fixes this issue by returning the same result as R:

test()
[1] 4 4 4

[eddelbuettel]

Florian, can we please try it the other way around as previously discussed:

• identify an issue
• create consensus that a code fix is needed
• work out a code fix
• create a pull request
• ensure the pull request is complete with
  • unit tests
  • documentation
  • ChangeLog entry

This one once again start from the wrong (though I agree that it is of course a very small one...).

[fplazaonate]

We briefly discussed this issue here #345 but I will create a new one

[eddelbuettel]

We can keep this open, it looks like a valid patch. I just do not like "random" pull requests that fly in without prior discussion. In this case, if #345 is/was indeed the place where this was discussed, then the fault is on me for not remembering -- and you for not referencing it. I have to deal with more than one discussion at a time, so helpful pointers are appreciated.

In any event, documentation, tests, changelog entries etc pp are also clearly missing from the PR. So please reopen and augment as you see fit.

[fplazaonate]

Could you have a look to my last commits?

[eddelbuettel]

The patch is fine as far as it mechanics go. But I can't make up my mind on this:

• on the hand it is nice to have a new subsetter
• but on the other hand it is a very specific case of recycling
  • what about vectors other than length one?
  • shouldn't an element other than position 0 be assignable?

Recycling has very specific meaning in R. We have avoided it here, mostly, as it is not natural for C++.

I am not yet convinced this really helps.

@kevinushey @jjallaire Any thoughts?

[kevinushey]

Looks good to me! The PR fixes a bug in the old implementation (the goal was to allow recycling in the first place; it just was not implemented correctly)

[eddelbuettel]

Thanks for that.

[eddelbuettel]

Ok, with this and the parallel email discussion this is good to go.