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

The possible reasons for getting this error are as follows:

When the if/while condition evaluates to NA.

For example:

> if(NA){}

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

> while(NA){}

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

When the argument passed is of length Zero.i.e.,

> if(NULL){}

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

When the condition resulted in something that could not be interpreted as logical.

For example:

 if("condition") {}

Error in if ("condition") { : argument is not interpretable as logical

When various values are passed in the condition.i.e.,

if (c(TRUE, FALSE)) {}

NULL

Warning message:

In if (c(TRUE, FALSE)) { :

  the condition has length > 1 and only the first element will be used