Enable e.g. 'a[b > 3] = b[b > 3]'

[thirdwing]

This for #345 .

It is just a combination of code from @kevinushey and @fabian-s .

I think converting to Vector is better than defining length() and get() for SubsetProxy.

[kevinushey]

Thanks!

What happens when we attempt to assign non-conforming types, e.g. if x is a NumericVector and y is an IntegerVector? We should have test cases that ensure these throw or convert properly (seems like it could be hairy)

[thirdwing]

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
IntegerVector subset_assign_subset(NumericVector x) {
    IntegerVector y(x.size());
    y[x > 3] = x[x > 3];
    return y;
}

/*

> Rcpp::sourceCpp("test.cpp")
> subset_assign_subset(1:6)
[1] 0 0 0 4 5 6
> x <- c(1.2, 2.3, 3.4, 4.5)
> subset_assign_subset(x)
[1] 0 0 3 4

*/

This can be added into unitTest, if necessary.

[kevinushey]

It looks like type coercion is already properly handled so I think this is good to go. E.g. this gives a compiler error, as hoped:

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
IntegerVector subset_assign_subset(CharacterVector x) {
  IntegerVector y(x.size());
  y[x > 3] = x[x > 3];
  return y;
}

[eddelbuettel]

Having a few unit tests would be nice. We have two so that is a start.

[eddelbuettel]

Appreciate the extra tests! Merging now.