### 13.1 FILTER

         FILTER BY var_name.
         FILTER OFF.

`FILTER` allows a boolean-valued variable to be used to select cases from the data stream for processing.

To set up filtering, specify `BY` and a variable name. Keyword BY is optional but recommended. Cases which have a zero or system- or user-missing value are excluded from analysis, but not deleted from the data stream. Cases with other values are analyzed. To filter based on a different condition, use transformations such as `COMPUTE` or `RECODE` to compute a filter variable of the required form, then specify that variable on `FILTER`.

`FILTER OFF` turns off case filtering.

Filtering takes place immediately before cases pass to a procedure for analysis. Only one filter variable may be active at a time. Normally, case filtering continues until it is explicitly turned off with `FILTER OFF`. However, if `FILTER` is placed after `TEMPORARY`, it filters only the next procedure or procedure-like command.