Vector class

[bartoszukm]

We should implement a vector class, using std:vector from C++, which would allow adding new items to a vector with amortized constant complexity (it would solve a "dynamically extending vector" problem).

The main question is: should it be a vector of any R objects (it would be like an R list), or maybe one type of objects (more like an R vector)?

And is there any way to implement operator [], like vector[5]? Or the only way is to make a function get_element(vector, 5) and set_element(vector, 5)?

[gagolews]

for []. you may overload the [.classname operator in R.

> x <- structure("test", class="testclass")
> "[.testclass" <- function(x, i)
+ stringi::stri_sub(x, i, length=1)
> x[1]
[1] "t"
> x[2]
[1] "e"

replacement version:

> "[<-.testclass" <- function(x, i, value) {
+ stringi::stri_sub(x, i, length=1) <- value
+ x
+ }
> x[1] <- ":P"
> x
[1] ":Pest"

vector of any R objects == list (in Rcpp, this will be std::vector<RObject>.

[bartoszukm]

Why do we use SEXP in stack and queue? Maybe we can also use RObject in stack and queue? Is it any difference?

[gagolews]

On 20.03.2015 09:38, Maciej Bartoszuk wrote:

Why do we use SEXP in stack and queue? Maybe we can also use RObject in stack and queue? Is it any difference?

RObject is a thin wrapper around an underlying SEXP. When storing data is concerned only , SEXP is better (more lightweight)

[bartoszukm]

Ok, I committed vector class in 1196208a9afd8718ffa269eec8f47db8516a27c4 .

Unfortunately, there are some issues in getting/setting one element, like at() or operator[].

Firstly, I tried as you said

"[.Vector" <- function(vec, i)
 {
    vector_at(vec,i) 
 }

 "[.Vector" <- function(vec, i, value)
 {
    vector_at(vec,i) = value #it's not working alone either, because R do not know about C++ references
 }

Unfortunately, R is detecting that it is an external pointer and forbid subsetting:

mv = vector_create(4)
mv[1]=5
mv[1]

Error in mv[1] = 5 : object of type 'externalptr' is not subsettable Error in mv[1] : object of type 'externalptr' is not subsettable

After that I tried to make something like that:

"vector_at<-" <- function(vec, i, value) {
    print(vec)
    print(i)
    print(value)
    vector_set_at(vec,i,value)
    print(vec)
    print(i)
    print(value)
 }

What is interesting, in this function everything is working fine, but... after function ends and returning to main code, which called "vector_at<-"... vector changes to random number, like NULL or 5.

Do you have any ideas?

For now, one can use vector_set_at(vec,i,value) and vector_at(vec,i) for setting and getting item at index i.

[gagolews]

Try setting  the class attribute by callling the class() function

Marek Gagolewski, PhD

Sent from Type Mail

On Mar 20, 2015, 11:30, at 11:30, Maciej Bartoszuk notifications@github.com wrote:

Ok, I committed vector class in 1196208a9afd8718ffa269eec8f47db8516a27c4 .

Unfortunately, there are some issues in getting/setting one element, like at() or operator[].

Firstly, I tried as you said

"[.Vector" <- function(vec, i)
{
   vector_at(vec,i) 
}

"[.Vector" <- function(vec, i, value)
{
vector_at(vec,i) = value #it's not working alone either, because R do
not know about C++ references
}

Unfortunately, R is detecting that it is an external pointer and forbid subsetting:

mv = vector_create(4)
mv[1]=5
mv[1]

Error in mv[1] = 5 : object of type 'externalptr' is not subsettable Error in mv[1] : object of type 'externalptr' is not subsettable

After that I tried to make something like that:

"vector_at<-" <- function(vec, i, value) {
   print(vec)
   print(i)
   print(value)
   vector_set_at(vec,i,value)
   print(vec)
   print(i)
   print(value)
}

What is interesting, in this function everything is working fine, but... after function end and returning to main code, which called "vector_at<-"... vector changes to random number, like NULL or 5.

Do you have any ideas?

For now, one can use vector_set_at(vec,i,value) and vector_at(vec,i) for setting and getting item at index i.

---

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