R - " missing value where TRUE/FALSE needed "

Question

I'm trying to execute the following code in R

comments = c("no","yes",NA)
for (l in 1:length(comments)) {
    if (comments[l] != NA) print(comments[l]);
}

But I'm getting an error

Error in if (comments[l] != NA) print(comments[l]) : missing value where TRUE/FALSE needed

What's going on here?

score 22 · Accepted Answer · answered Nov 19 '14 at 13:50

22

check the command : NA!=NA : you'll get the result NA, hence the error message.

You have to use the function is.na for your ifstatement to work (in general, it is always better to use this function to check for NA values) :

comments = c("no","yes",NA)
for (l in 1:length(comments)) {
    if (!is.na(comments[l])) print(comments[l])
}
[1] "no"
[1] "yes"

answered Nov 19 '14 at 13:50

Cath

1

...check NA with is.na(), and in my case, accept the brutal reality that it's not NULL and that both NA and NULL exist. – Chris Feb 13 '18 at 15:42
@Chris there is a `is.null` function though ;-) – Cath Feb 13 '18 at 15:44

score 5 · Answer 2 · answered Nov 19 '14 at 13:50

5

Can you change the if condition to this:

if (!is.na(comments[l])) print(comments[l]);

You can only check for NA values with is.na().

answered Nov 19 '14 at 13:50

Nikos

2

@user3582590: please consider accepting answers that actually answer your question, by clicking the little checkmark under the vote count of the answer. This identifies the most helpful answers for future readers. – Stephan Kolassa Nov 19 '14 at 13:53

2 Answers2