'The R Inferno' page 59.
Patrick Burns
patr...@burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of "The R Inferno" and "A Guide for the Unwilling S User")
mau...@alice.it wrote:
I can define a list containing NULL elements:
myList <- list("aaa",NULL,TRUE)
names(myList) <- c("first","second","third")
myList
$first
[1] "aaa"
$second
NULL
$third
[1] TRUE
length(myList)
[1] 3
However, if I assign NULL to any of the list element then such
element is deleted from the list:
myList$second <- NULL
myList
$first
[1] "aaa"
$third
[1] TRUE
length(myList)
[1] 2
#
myList$first <- NULL
myList
$third
[1] TRUE
length(myList)
[1] 1
Instead vectors cannot include NULL element:
vec <- c(TRUE,NULL,FALSE)
vec
[1] TRUE FALSE
length(vec)
[1] 2
vec[1] <- NULL
Error in vec[1] <- NULL : replacement has length zero
Is the above shown behaviour of list data structures to be expected ?
I took me a lot of sweat to figure out this wierd behaviour was the cause of a bug
in my big program.
In general, if I have a list with some elements initialized to NULL, that can be changed
dynamically, then how can I reinitialize such elements to NULL without deleting them
from the list ?
Thank you in advance,
Maura
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