Our interference from then environment issue was a bit subtle. But there are variations that can be a bit more insidious.
Please consider the following.
library("dplyr") # unrelated value that happens # to be in our environment z <- "y" data.frame(x = 1, y = 2, z = 3) %>% select(-z) # x y # 1 1 2 data.frame(x = 1, y = 2) %>% # oops, no "z" select(-z) # x # 1 1 # notice column "y" was removed and # no error or warning was signalled.
data.frame has a lot of columns, and is coming from somewhere else (even as an argument to a function): we may not notice the column loss until very much later (making for hard debugging or even unreliable results).