r - Error in if/while (condition) {: missing Value where TRUE/FALSE needed -

i received error message:

error in if (condition) { : missing value true/false needed 

or

error in while (condition) { : missing value true/false needed 

what mean, , how prevent it?

the evaluation of condition resulted in na. if conditional must have either true or false result.

if (na) {} ## error in if (na) { : missing value true/false needed 

this can happen accidentally results of calculations:

if(true && sqrt(-1)) {} ## error in if (true && sqrt(-1)) { : missing value true/false needed 

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to test whether object missing use is.na(x) rather x == na.

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see related errors:

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

error in if/while (condition) : argument not interpretable logical

if (null) {} ## error in if (null) { : argument of length 0  if ("not logical") {} ## error: argument not interpretable logical  if (c(true, false)) {} ## warning message: ## condition has length > 1 , first element used