Working with Empty Cells in Expressions

At any given time, some of the cells of an analytic workspace data object may be empty. An empty cell occurs when a specific data value has not been assigned to it or when a data value cannot be calculated for the cell. The value of any empty cell in an object is NA. An NA value has no specific data type. Certain functions (for example, the aggregation functions) return an NA values when the information that is requested with the function is not available or cannot be calculated. Similarly, an expression whose value cannot be calculated has NA as its value.

Specifying a Value of NA

There are cases in which you might specify an operation for which no data is available. For example, there might be no appropriate value for a given cell in a variable, for the return value of a function, or for the value of an expression that includes an arithmetic operator. In these cases, an NA (Not Available) value is automatically supplied.

To set the values of a variable or relation to NA, you can use an assignment statement (SET), as shown in the following example.

sales = NA

Controlling how NA values are treated

A number of options and functions control how NA values are treated. For example:

The options listed in Table A-15, "NA and Nonexistent Value Options".
The NAFILL function returns the values of the source expression with any NA values appearing as the specified fill expression. You can include this function in an expression to control the format of its value.
System properties listed in Table A-2, "System Properties Used When Working with NA Values".