Conditional Logic

GTL supports conditional logic that enables you to include or exclude one or more GTL statements at run time:

IF ( condition )

GTL statement(s);

ELSE

GTL statement(s);

ENDIF ;

The IF statement requires an ENDIF statement, which delimits the IF block. The IF block can be placed anywhere within the BEGINGRAPH / ENDGRAPH block.

The condition is an expression that evaluates to a numeric constant, where all numeric constants other than 0 and MISSING are true. The IF block is evaluated with an implied EVAL( condition ), so it is not necessary to include an EVAL as part of the condition.

Note: Dynamic variables that are initialized to an ODS-recognized value, such as YES, NO, TRUE, or FALSE, do not work as expected when used as an expression in an IF-THEN statement. In that case, the expression is treated as a string, which always evaluates to a positive integer value (FALSE).

Here are some examples:

/* test a computed value */
if (weekday(today()) in (1 7))
   entrytitle "Run during the weekend";
else
   entrytitle "Run during the work week";
endif;

/* test for the value of a numeric dynamic */
if ( ADDREF > 0 )
   referenceline y=1;
   referenceline y=0;
   referenceline y=-1;
endif;

/* test for the value of a character dynamic */
if ( upcase(ADDREF) =: "Y")
   referenceline y=1;
   referenceline y=0;
   referenceline y=-1;
endif;

/* test whether a dynamic is initialized */
if (exists(ADDREF))
   referenceline y=1;
   referenceline y=0;
   referenceline y=-1;
endif;

The GTL conditional logic is used only for determining which statements to render. It is not used to control what is in the data object. In the following example, the data object contains columns for DATE, AMOUNT, and LOG10(AMOUNT), but only one scatter plot is created.

if ( LOGFLAG )
  scatterplot x=date y=amount;
else
  scatterplot x=date y=eval(log10(amount));
endif;

For the conditional logic in GTL, it is seldom necessary to test for the existence of option values that are set by columns or dynamics. Consider the following statement:

scatterplot x=date y=amount / group=GROUPVAR;

This SCATTERPLOT statement is equivalent to the following code because option values that are set by columns that do not exist, or by dynamics that are uninitialized, simply "drop out" at run time and do not produce errors or warnings:

if ( exists(GROUPVAR) )
  scatterplot x=date y=amount / group=GROUPVAR; 
else
  scatterplot x=date y=amount;
endif;

The GTL code that is specified in the conditional block must contain complete statements and / or complete blocks of statements. For example, the following IF block produces a compile error because there are more LAYOUT statements than ENDLAYOUT statements:

/* produces a compile error */
if ( exists(SQUAREPLOT) )
  layout overlayequated / equatetype=square;
else 
  layout overlay;
endif;

    scatterplot x=XVAR y=YVAR;
endlayout;

The following logic is the correct conditional construct:

if ( exists(SQUAREPLOT) )
  layout overlayequated / equatetype=square;
    scatterplot x=XVAR y=YVAR;
  endlayout;
else
  layout overlay;
    scatterplot x=XVAR y=YVAR;
  endlayout;
endif;

GTL does not provide ELSE IF syntax, but you can create a nested IF/ ELSE block as follows:

IF ( condition )

GTL statement(s);

ELSE

IF ( condition )

GTL statement(s);

ELSE

GTL statement(s);

ENDIF ;

The following example creates a generalized histogram that conditionally shows the variable label and combinations of fitted distribution curves:

proc template;
  define statgraph conditional;
    dynamic NUMVAR "required" SCALE CURVE;
    begingraph;
      entrytitle "Distribution of  " eval(colname(NUMVAR));

      if ( colname(NUMVAR) ne collabel(NUMVAR) )
        entrytitle "(" eval(collabel(NUMVAR)) ")";
      endif;

      layout overlay / xaxisopts=(display=(ticks tickvalues line));
        histogram NUMVAR / scale=SCALE;

        if ( upcase(CURVE) in ("ALL" "NORMAL" ) )
          densityplot NUMVAR / normal() name="N"
            lineattrs=GraphData1 legendlabel="Normal Distribution";
        endif;

        if ( upcase(CURVE) in ("ALL" "KDE" "KERNEL") )
          densityplot NUMVAR / kernel() name="K"
            lineattrs=GraphData2 legendlabel="Kernel Density Estimate";
        endif;
        discretelegend "N" "K";
      endlayout;

    endgraph;
  end;
run;

The DYNAMIC statement identifies the dynamic variables.
The first IF block specifies an ENTRYTITLE statement that is conditionally executed if the column name differs from the column label.
The next two IF blocks evaluate the value of the dynamic variable CURVE. If CURVE is not used, the code in the conditional blocks is not executed. If CURVE is initialized to one of the strings "all" or "normal" in any letter case, then the first DENSITYPLOT statement is executed. If CURVE is initialized to one of the strings "all", "kde", or "kernel" in any letter case, then the second DENSITYPLOT statement is executed. Thus, the results of the conditional logic determine whether zero, one, or two density plots are generated in the graph.
Constructing the legend does not require conditional logic because any referenced plot names that do not exist are not used.

After submitting the template code, we can execute the template with various combinations of dynamic values.

In this first execution, the NUMVAR dynamic is initialized with a column that has a defined label, so two title lines are generated. The first title line displays the column name, and the second title line displays the column label. The CURVE dynamic is not initialized, so the template does not generate a density plot.

proc sgrender data=sashelp.heart template=conditional;
  dynamic numvar="mrw";
run;

Both the Variable and Label Appear in the Title

In this next execution of the template, the NUMVAR dynamic is initialized with a column that does not have a label, so only a single title line is displayed in the graph. The CURVE dynamic is initialized with the value "kde", so in addition to the histogram, the template generates a kernel density estimate.

proc sgrender data=sashelp.heart template=conditional;
  dynamic numvar="cholesterol" curve="kde";
run;

In this final execution of the template, the CURVE dynamic is initialized with the value "all", so in addition to the histogram, the template generates a normal density estimate and a kernel density estimate.

proc sgrender data=sashelp.heart template=conditional;
  dynamic numvar="cholesterol" scale="count" curve="all";
run;

Graph with both a Normal and a Kernel Density Estimate

The value of the SCALE dynamic does not need to be verified. If it is not one of COUNT, DENSITY, PERCENT, or PROPORTION (not case sensitive), the default scale is used with no warning or error.