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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.
When the 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).
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