Error in eval(expr, envir, enclos) when using rmongodbHelper - r

Question

I'm working with rmongodb and rmongodbHelper packages and i've built this function.
CUPS_CP_TAR36 <- function(codi,cant){
cups <- vector()
query <- json_to_bson('{"clLst.U_COD_POSTAL": codi, "clLst.TARIFA_ATR": {"$in": "3.0A","3.1A","6.1"]}}')
output <- json_to_bson('{"id":1}')
cursor <- mongo.find(mongo, sips, query, fields=output, limit=cant)
k = 0
while(mongo.cursor.next(cursor)){
k = k + 1
cups[k] <- mongo.bson.value(mongo.cursor.value(cursor), "_id")
}
return(cups)
}
but when I try to use it:
example <- CUPS_CP_TAR36(codi="08036", cant=10)
I get the following error and really dont know why, i'm not used to write my own functions:
Error in eval(expr, envir, enclos) : object 'codi' not found
Thanks!

Answer 1

Try latest rmongodb version from github. bson from json works out of the box. Moreover mongo.bson.to.list works fine for every case, so you dont't need to construct bson from json. I have plans to push new version of the package to CRAN next week.
library(devtools)
install_github("mongosoup/rmongodb")

Answer 2

query <- json_to_bson('{"clLst.U_COD_POSTAL": codi, ...}')
json_to_bson() expects a JSON string. The string you provide is not valid JSON, just as {"key":val} is not valid - while {"key":"val"} or {"key":3.14} are valid.
Of course codi isn't even intended by you to be a string in your case but to be a variable. But as you write the code there is no way for R to know about that.
So you might write:
query <- json_to_bson(sprintf('{"clLst.U_COD_POSTAL": "%s", ...}',codi))
The equivalent expression with your value of codi is then:
query <- json_to_bson('{"clLst.U_COD_POSTAL": "08036", ...}')
The reason why there is an error message involving eval() is b/c I wrote the interpretation of the JSON very, very simple - mind this "package" is merely a workaround and hopefully superfluous very soon.
The JSON is turned into a list()-expression using string-substitution and then eval()ed.
rmongodbHelper / R / json_to_list.R:
json_to_list <- function(json) {
json <- gsub("\n","",json)
json <- gsub("\\{\\}","list()",json)
[...]
json <- gsub("\\$","_$",json)
return(eval(parse(text = json)))
}
Further details: MongoDB – State of the R