GAMS Data Exchange API

Reading data using a filter
Page 6
After reading the data, we print the number of records that were skipped in the read routine.
.
1.2.4 Reading data using a filter
Reading data using a filter allows us to control the action for every index position. The type of action is specified using action
codes and needs to be specified for every index position. The actual reading of the records is done with the gdxDataReadMap (
see page 76) function.
Action code
UnMapped (-2) No mapping is performed; the value of the unique element is the value as stored in the GDX file.
Use gdxUMUelGet ( see page 92) to get the string representation.
Checked (0) Map the unique element value to the user defined value. Use gdxGetUEL ( see page 85) to get
the string representation. If a user mapping was not defined for this element , the record is flagged
as an error record and the record will be skipped.
Expand (-1) Map the unique element value to the user defined value. Use gdxGetUEL ( see page 85) to get
the string representation. If a user mapping was not defined for this element, define a user
mapping automatically using the next higher user map value.
Filter Number
(>0)
Map the unique element value to the user defined value. Use gdxGetUEL ( see page 85) to get
the string representation. If the element is not enabled in the filter for this index position, the record
is flagged as an error record and it will be skipped. The filter number is specified using the
gdxFilterRegisterStart ( see page 82) function.
Refering to the following GAMS fragment, we want to read the parameter A. The set I is the domain for the first index; there is no
domain for the second index position:
Set I /.../;
Parameter A(I,*);
Assuming we have read set I already, the following code snapshot illustrates how to read parameter A.
// Register the filter for set I; reference this filter with integer 123
if not gdxFilterRegisterStart(PGX,123)
then
ReportGDXError(PGX);
gdxFilterRegister(PGX,1000);
gdxFilterRegister(PGX,2000);
if not gdxFilterRegisterDone(PGX)
then
ReportGDXError(PGX);
// set the filter
Filt[1] := 123; //filter for I
Filt[2] := -1; // expand
GDX GAMS Data Exchange Reading data
from a GDX file
// Remember highest mapped value in variable LastMapped
gdxUMUelInfo(PGX,NrUnMapped,LastMapped);
// Read parameter A as a 2 dimensional parameter
if not gdxFindSymbol(PGX,'A',SyNr)
then
begin
WriteLn('**** Could not find symbol A');
halt;
end;
GAMS Data Exchange API
1.2
Page 6 2.4
12/3/2012