possible bug: NULL equality in lists.
Uwe Ligges wrote:
Seth Falcon wrote:
Uwe Ligges <ligges at statistik.uni-dortmund.de> writes:
Charles Dupont wrote:
I was messing around with R and I found an example R behaving oddly: a <- alist(NULL, "bob", c(3,6,2,3)) a a == 'NULL' a == "NULL" a == 'cat'
Always use is.null() to test on NULL, as in:
What should I do if I want to check for the string "NULL"?
These are all dangerous, hence use the "safe" ways: sapply(a, is.null) sapply(a, identical, "NULL") sapply(a, is.na) sapply(a, identical, "NA") Best, Uwe
For the NA list problem. It would be better if 'as.character' when converting a list when it finds a NA value to set that element to the string NA value not "NA" the string. Charles
a <- list(NULL, "NULL", NA, "NA")
a == "NULL"
[1] TRUE TRUE FALSE FALSE
a == "NA"
[1] FALSE FALSE TRUE TRUE These are because of as.character:
as.character(a)
[1] "NULL" "NULL" "NA" "NA" Yet,
as.character(NULL)
character(0)
as.character(NA)
[1] NA + seth
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Charles Dupont Computer System Analyst School of Medicine Department of Biostatistics Vanderbilt University