Hi,
Set Operations Using Bit Sequences
If you have a set of m elements, you can represent any subset as a sequence of bits. If the nth element of the set is present in a subset, the n th bit is set to 1, otherwise, it is set to 0. The universal set therefore contains no zeros.
In ABAP, you can represent a set of m elements using a field with type X and length of at least m/8. To include a member of the universal set in a set, use the SET BIT statement. To check which members of the universal set are included in a particular set, use the GET BIT statement. You can use bit operations for the following set operations:
Set operation
Bit operation
Intersection
BIT-AND
Union
BIT-OR
Symmetrical difference
BIT-XOR
You can also use the O operator when comparing bit sequences to determine whether a particular set is a subset of another.
DATA: FRANKFURT(4) TYPE X,
FRISCO(4) TYPE X,
INTERSECT(4) TYPE X,
UNION(4) TYPE X,
BIT TYPE I.
DATA: CARRID TYPE SPFLI-CARRID,
CARRIER LIKE SORTED TABLE OF CARRID
WITH UNIQUE KEY TABLE LINE.
DATA WA TYPE SPFLI.
SELECT CARRID FROM SCARR INTO TABLE CARRIER.
SELECT CARRID CITYFROM FROM SPFLI
INTO CORRESPONDING FIELDS OF WA.
WRITE: / WA-CARRID, WA-CITYFROM.
READ TABLE CARRIER FROM WA-CARRID TRANSPORTING NO FIELDS.
CASE WA-CITYFROM.
WHEN 'FRANKFURT'.
SET BIT SY-TABIX OF FRANKFURT.
WHEN 'SAN FRANCISCO'.
SET BIT SY-TABIX OF FRISCO.
ENDCASE.
ENDSELECT.
INTERSECT = FRANKFURT BIT-AND FRISCO.
UNION = FRANKFURT BIT-OR FRISCO.
SKIP.
WRITE 'Airlines flying from Frankfurt and San Francisco:'.
DO 32 TIMES.
GET BIT SY-INDEX OF INTERSECT INTO BIT.
IF BIT = 1.
READ TABLE CARRIER INDEX SY-INDEX INTO CARRID.
WRITE CARRID.
ENDIF.
ENDDO.
SKIP.
WRITE 'Airlines flying from Frankfurt or San Francisco:'.
DO 32 TIMES.
GET BIT SY-INDEX OF UNION INTO BIT.
IF BIT = 1.
READ TABLE CARRIER INDEX SY-INDEX INTO CARRID.
WRITE CARRID.
ENDIF.
ENDDO.
This produces the following output list:
AA NEWYORK
AA SANFRANSISCO
AZ ROME
AZ ROME
AZ TOKYO
AZ ROME
DL NEWYORK
DL SANFRANSISCO
The program uses four hexadecimal fields with length 4 - FRANKFURT, FRISCO, INTERSECT, and UNION. Each of these fields can represent a set of up to 32 elements. The basic set is the set of all airlines from database table SCARR. Each bit of the corresponding bit sequences representes one airline. To provide an index, the external index table CARRIER is created and filled with the airline codes from table SCARR. It is then possible to identify an airline using the internal index of table CARRIER.
In the SELECT loop for database table SPFLI, the corresponding bit for the airline is set either in the FRANKFURT field or the FRISCO field, depending on the departure city. The line number SY-TABIX is determined using a READ statement in which no fields are transported.
The intersection and union of FRANKFURT and FRISCO are constructed using the bit operations BIT-AND and BIT-OR.
The bits in INTERSECT and UNION are read one by one and evaluated in two DO loops. For each position in the fields with the value 1, a READ statement retrieves the airline code from the table CARRIER.
<REMOVED BY MODERATOR>
Cheers,
Chandra Sekhar.
Edited by: Alvaro Tejada Galindo on Mar 4, 2008 2:50 PM
Bluesky
