R Error - cannot change value of locked binding for 'df'

Question

I\'m trying to filter some data, with functions in R relatives to data frames. But in the second function, it gives me the following error: cannot change the value of locked bin

Answer 1

Sometimes, one does want to violate the spirit of functional languages.

I am not sure why, in R, a locked function prevents you from creating a variable at the same level, but the problem the OP has is because the function df() is locked in an environment above that of the current environment (which <<- finds).

Here is some code (probably not the best) to find the environment in which df is (already) bound (i.e., already exists), and then check to see if it is, in fact, locked in that environment.

> x <- environment(); while(TRUE) { print(exists("df", x)); x <- parent.env(x) }
[1] TRUE
[1] TRUE
[1] TRUE
[1] FALSE
[1] FALSE
[1] FALSE
[1] FALSE
[1] FALSE
[1] FALSE
[1] FALSE
[1] FALSE
Error in parent.env(x) : the empty environment has no parent
> bindingIsLocked("df", parent.env(parent.env(environment())))
[1] TRUE
> 

In this case, creating a variable df in the "global" context should solve the problem. i.e.,

df <- NULL

filter.data = function(x, dir = ".") {
    load.data(x, dir)
    df <<- dados_reais[,c(1,2,3,4,9,10,12)]
}

Alternatively, changing the name of the variable (from df, say, to myveryowndf) should also fix the problem.