Aqui está o código que tentei, tentei maneiras. Basicamente, estou apenas me perguntando sobre a parte da permissão negada.

 data <- matrix(c(1,2,3,4), ncol=2)
 write.csv(data,"C:/Users/brian_000/Documents")

Erro:

Error in file(file, ifelse(append, "a", "w")) : 
  cannot open the connection
 In addition: Warning message:
 In file(file, ifelse(append, "a", "w")) :
   cannot open file 'C:/Users/brian_000/Documents': Permission denied
   write.csv(data, file="C:/Users/brian_000/Documents")
  Error in file(file, ifelse(append, "a", "w")) : 
 cannot open the connection
 In addition: Warning message:
 In file(file, ifelse(append, "a", "w")) :
  cannot open file 'C:/Users/brian_000/Documents': Permission denied