MASK without parameters is an operation which leads to the activation
procedure for the fields of any Survo data file. (Another way to
start the selection and activation procedure is to press key FILE_ACT, but
this does not update any MASK line in the edit field.)
After return from MASK procedure to normal edit mode the current
line will contain a MASK specification of the form
MASK=--XX-A-YX-R---AA- (for example)
indicating the activated fields in the current data file.
If a MASK specification appears in the current subfield,
when a statistical operation like CORR,LINREG,TAB etc. is activated,
it determines the roles of the variables in the analysis.
However, a possible VARS specification always overrides MASK in
statistical operations (See VARS?).
By activation of a MASK line with a given mask string (MASK=--XX-A-- ,
for example) the selection of the fields determined by that string will
be shown for a selected file and this selection may be adjusted. After
return to edit mode again the MASK line will show the latest selection.
Since a data file can contain several optional mask columns (default
number is 7), any of them can be used to indicate the selected vari-
ables by giving its number #1,#2,#3,,, as MASK=#7.
A partial selection according to a mask column is also possible. For
example, MASK=#7(XY) selects the fields indicated by X or Y in mask
column 7.
Activation of a MASK line of this type will lead to a file activation
display of that mask column for additional changes.
M = Setting masks by FILE MASK
V = More information on selection of variables
Help System (web edition)