Logical Grouping of Filter Tests

Relational Tests

Selection Set Filter Lists

Selection Set Manipulation

 

AutoLISP Developer's Guide > Using the AutoLISP Language > Using AutoLISP to Manipulate AutoCAD Objects > Selection Set Handling > Selection Set Filter Lists > 

Logical Grouping of Filter Tests

You can also test groups by creating nested Boolean expressions that use the logical grouping operators shown in the following table:

The grouping operators are specified by -4 groups, like the relational operators. They are paired and must be balanced correctly in the filter list or the ssget call will fail. An example of grouping operators in a filter list follows:

(ssget "X" 

    
 '(
    
    (-4 . "<OR")
    
      (-4 . "<AND")
    
        (0 . "CIRCLE")
    
        (40 . 1.0)
    
      (-4 . "AND>")
    
      (-4 . "<AND")
    
        (0 . "LINE")
    
        (8 . "ABC")
    
      (-4 . "AND>")
    
    (-4 . "OR>")
    
  )
    
)
  

This code selects all circles with a radius of 1.0 plus all lines on layer "ABC". The grouping operators are not case-sensitive; for example, you can specify "and>", "<or", instead of "AND>", "<OR".

Grouping operators are not allowed within the -3 group. Multiple application names specified in a -3 group use an implied AND operator. If you want to test for extended data using other grouping operators, specify separate -3 groups and group them as desired. To select all circles having extended data for either application "APP1" or "APP2" but not both, enter the following:

(ssget "X" 

 '((0 . "CIRCLE")

    (-4 . "<XOR")

      (-3 ("APP1"))

      (-3 ("APP2"))

    (-4 . "XOR>")

  )

)

You can simplify the coding of frequently used grouping operators by setting them equal to a symbol. The previous example could be rewritten as follows (notice that in this example you must explicitly quote each list):

(setq <xor '(-4 . "<XOR") 

       xor> '(-4 . "XOR>") )

(ssget "X" 

  (list 

    '(0 . "CIRCLE")

    <xor

      '(-3 ("APP1"))

      '(-3 ("APP2"))

    xor>

  )

)

As you can see, this method may not be sensible for short pieces of code but can be beneficial in larger applications.