[R] how to add comma to string vector?

[Luigi Marongiu]

Hello,
I need to convert an R vector to a python array. Essentially, I got a
vector of strings where each element must be enclosed in single
quotes. The problem is that each closing single quote should contain a
comma. What is the regex trick to do that?
I tried with:
```
> (raws = c("field_1", "field_2",  "field_3"))
[1] "field_1" "field_2" "field_3"
> (items = sQuote(raws))
[1] "'field_1'" "'field_2'" "'field_3'"
> gsub("\'[:blank:]", "\',[:blank:]", items,  ignore.case = FALSE, perl = FALSE)
[1] "'field_1'" "'field_2'" "'field_3'"
> cat("python_Array = [", domain_list, "]\n")
python_Array = [ 'Index' 'Endpoints' 'Confounders' 'Arboexposure' ]
```
To note that `python_Array` does not have commas between elements and
`gsub` did not do anything...

Thank you