[Rcpp-devel] Negative vector lengths from rep_each()

[Barth Riley]

Dear list

I have written the following function to produce multidimensional arrays using Rcpp:

NumericVector arrayFromVector(NumericVector input, IntegerVector dim) {

// check for zero-length vectors
if(dim.length() == 0 || input.length() == 0) {
return NULL;
}

long p = 1;
for(int i = 0; i < dim.length(); i++) {
p *= dim[i];
}

if((input.length() == 1) & (p > 1)) {
input = Rcpp::rep_each(input, p);
} else if (input.length() != p) {
return NULL;
}

input.attr("dim") = dim;
return input;
}


This function usually produces the desired result, but in some cases (it seems with relatively large vector lengths) I get the error “negative length vectors are not allowed.” The error occurs on the line:

input = Rcpp::rep_each(input, p);

I changed p from an int to a long, thinking I was encountering an overflow issue. But this did not resolve the problem. The test vector contains 45,000 values.

Any suggestions?

Thanks in advance

Barth


Sent from Mail for Windows 10

[Dirk Eddelbuettel]

On 29 October 2018 at 09:12, Barth Riley wrote:
| Dear list
|
| I have written the following function to produce multidimensional arrays using Rcpp:
|
| NumericVector arrayFromVector(NumericVector input, IntegerVector dim) {
|
| // check for zero-length vectors
| if(dim.length() == 0 || input.length() == 0) {
| return NULL;
| }
|
| long p = 1;
| for(int i = 0; i < dim.length(); i++) {
| p *= dim[i];
| }
|
| if((input.length() == 1) & (p > 1)) {
| input = Rcpp::rep_each(input, p);
| } else if (input.length() != p) {
| return NULL;
| }
|
| input.attr("dim") = dim;
| return input;
| }
|
|
| This function usually produces the desired result, but in some cases (it seems with relatively large vector lengths) I get the error “negative length vectors are not allowed.”

That probably means integer overflow. Integers are "just" 32 bit so this may
happen. R itself uses an "extended" type for this, which is really a double
with larger range.

I would recommend you test for that value.

| input = Rcpp::rep_each(input, p);
|
| I changed p from an int to a long, thinking I was encountering an overflow issue. But this did not resolve the problem. The test vector contains 45,000 values.

It's not the number of values, but their values.

| Any suggestions?

If you need multidimensional arrays and can use C++14 you may find the
xtensor package useful:

https://cran.r-project.org/web/packages/xtensor/index.html

Dirk

| Thanks in advance
|
| Barth
|
|
| Sent from Mail for Windows 10
|
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