R Error: missing value where true/false needed

Encountering the occasional error message is a common part of the programming and this one results from a failure to properly define the input into an “if statement” or “while statement” as either true or false. It is an easy error to make, but also easy to correct.

Circumstances of this error message.

You will get this error message if the value you are putting into an “if statement” or “while statement” is not available (NA). When this occurs, these statements cannot process the data resulting in an error message. Here is a simple example of a code that produces this error message.

# source: R Error: Missing value where true/false needed
 > x = NA
 > if(x) {x}
 Error in if (x) { : missing value where TRUE/FALSE needed

As you can tell the variable “x” has a value of “NA” it has a result it triggered the error message.

Reason for this error message.

The reason why this error message occurs is that you are passing an invalid value to “if statement” or “while statement.” These statements simply check to see if the argument is true or false. If the value it gets is not one of these, it will produce an error message. This is actually one of the simplest error messages to understand. Not only is there a message simple, but it gives meaningful information. This means the error message is useful in helping to understand what is going on.

How to fix this error message.

The fix for this error is quite simple. All you need to do embed your “if statement” or “while statement” in another “if statement” that puts the value through the is.na() function to see if its value is “NA” or not. This will allow you to avoid this error message, as illustrated below.

# solution: Missing value where true/false needed
> x = NA
> if(is.na(x)) {x=FALSE} else {if(x) {x}} 

Now that this simple little check, not only does it avoids the error message, but it provides you a way the correct the error when it occurs. Once the error has been detected, you can use it to define the value of the variable being checked who wrote it is no longer “NA” and causes no further problems. In our example above, because the value of “x” becomes “FALSE.” The result is that we have not just bypassed the error what about you corrected it.

# solution - bypassing error: Missing value where true/false needed
 > x = TRUE
 > if(is.na(x)) {x=FALSE} else {if(x) {x}} 
 [1] TRUE

The second example shows the results of the corrected version if x is true. This is because if x is true, it doesn’t have a value of “NA” and so the first “if statement” is false. This means that it gets passed on to the second “if statement” that detects the value of “x” as being “TRUE” and it prints the value of “x.” This is an easy error message to both understand and correct. Correcting it simply involves detecting “NA” value before going through the “if statement.”