represents data that is missing.
specifies a reason for the data's being missing.
associates the expression expr with the missing data.
- Missing[…] is a symbolic object, with no default evaluation rules defined.
- Typical examples of "reason" include "NotApplicable", "Unknown", "NotAvailable", "Nonexistent", "Indeterminate", "Variable", "Disputed", or "TooLarge".
- Missing can be returned by most data functions, such as CountryData and ElementData.
- Missing is returned when a key requested in an Association is not found.
- Plotting functions automatically omit Missing objects when plotting data.
- In TraditionalForm, Missing is typically formatted as —, with a tooltip specifying the reason.
When properties are missing, a Missing object is returned:
Missing is generated when an association does not contain the specified key:
Missing elements can be filtered out using DeleteCases:
Visualization typically automatically filters out Missing elements: