Replacing each element of any object - r

Question

Is there any clever way to replace each part of any object with some values (for example NA's).
Let's take those objects
obj1 <- t.test(1:10)
obj2 <- matrix(1:9, 3)
obj3 <- 1:10
obj4 <- list(a = 1:10, b = letters[1:5], c = as.factor(1:10))
the expected output would be similar to
for (i in 1:length(obj1)) obj1[[i]] <- rep(NA, length(obj1[[i]]))
obj2 <- matrix(rep(NA, 9), 3)
obj3 <- rep(NA, 10)
obj4 <- list(a = rep(NA, 10), b = rep(NA, 5), c = rep(NA, 10))
So no matter if an object is a list, matrix, data.frame, vector etc. each part of the object is to be replaced with NA.
Is there any clever way to do so that does not need multiple loops, checking for object type every time and lots of exceptions (if (is.list(part)) ... etc.)?

Answer 1

You can take advantage of the fact that using an empty extraction index during assignment (i.e., x[] <- NA) replaces all elements with the right-hand side value. In your case, you could do something like this using rapply to attack all elements of all objects:
> rapply(mget(ls()), function(x) x[] <- rep(NA, length(x)), how = "replace")
$obj1
$obj1$statistic
[1] NA
$obj1$parameter
[1] NA
$obj1$p.value
[1] NA
$obj1$conf.int
[1] NA NA
$obj1$estimate
[1] NA
$obj1$null.value
[1] NA
$obj1$alternative
[1] NA
$obj1$method
[1] NA
$obj1$data.name
[1] NA
$obj2
[1] NA NA NA NA NA NA NA NA NA
$obj3
[1] NA NA NA NA NA NA NA NA NA NA
$obj4
$obj4$a
[1] NA NA NA NA NA NA NA NA NA NA
$obj4$b
[1] NA NA NA NA NA
$obj4$c
[1] NA NA NA NA NA NA NA NA NA NA
That's a very simple solution, though. You could probably complicate the function being passed to rapply so that it used S3 method dispatch to identify what class of object it was seeing and possibly return a different data structure (e.g., data.frame or matrix) accordingly, rather than just a vector of NAs.