Question

I received this error message:

Error in if (condition) { : missing value where TRUE/FALSE needed

or

Error in while (condition) { : missing value where TRUE/FALSE needed

What does it mean, and how do I prevent it?

Answer 1

The evaluation of condition resulted in an NA. The if conditional must have either a TRUE or FALSE result.

if (NA) {}
## Error in if (NA) { : missing value where TRUE/FALSE needed

This can happen accidentally as the results of calculations:

if(TRUE && sqrt(-1)) {}
## Error in if (TRUE && sqrt(-1)) { : missing value where TRUE/FALSE needed

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To test whether an object is missing use is.na(x) rather than x == NA.

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See also the related errors:

Error in if/while (condition) { : argument is of length zero

Error in if/while (condition) : argument is not interpretable as logical

if (NULL) {}
## Error in if (NULL) { : argument is of length zero

if ("not logical") {}
## Error: argument is not interpretable as logical

if (c(TRUE, FALSE)) {}
## Warning message:
## the condition has length > 1 and only the first element will be used