R -“需要TRUE/FALSE时缺失值”[重复]

This question already has an answer here:

这个问题已经有了答案:

• Error in if/while (condition) {: missing Value where TRUE/FALSE needed 2 answers
• if/while (condition){:缺失值，其中TRUE/FALSE需要2个答案

I'm trying to execute the following code in R

我试着用R执行下面的代码

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

But I'm getting an error

但是我有一个错误。

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

What's going on here?

这是怎么回事?

2 个解决方案

#1

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

检查命令:NA!=NA:您将得到结果NA，从而得到错误消息。

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) :

你必须使用函数is。为了使ifstatement起作用(一般来说，最好使用此函数检查na值):

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

#2

Can you change the if condition to this:

能否将if条件改为:

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

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

只能使用is.na()检查NA值。