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Processing Variables with Arrays
Creating Multidimensional Arrays


When this DATA step is compiled, the program data vector is created containing the variables Year, Month1 through Month12, and the new variables Qtr1 through Qtr4. (Only the beginning and ending portions of the program data vector are represented here.) 
     data finance.quarters(drop=i j);
        set finance.monthly;
        array m(4,3) month1-month12;
        array Qtr(4);
        do i=1 to 4;
          qtr(i=0);
           do j=1 to 3;
              qtr(i)+m(i,j);
           end;
        end;
     run;

Program Data Vector

During the initial execution of the DATA step, the values of the first observation of Finance.Monthly are read into the program data vector. When the first DO loop executes the first time, the index variable i is set to 1. 
     data finance.quarters(drop=i j);
        set finance.monthly;
        array m(4,3) month1-month12;
        array Qtr(4);
      > do i=1 to 4;          i=1
          qtr(i=0);
           do j=1 to 3;
              qtr(i)+m(i,j);
           end;
        end;
     run;

Program Data Vector

During the first iteration of the nested DO loop, the value of Month1, referenced by m(i,j), is added to Qtr1. 
     data finance.quarters(drop=i j);
        set finance.monthly;
        array m(4,3) month1-month12;
        array Qtr(4);
        do i=1 to 4;          i=1
          qtr(i=0);
         > do j=1 to 3;       j=1
              qtr(1)+m(1,1);
           end;
        end;
     run;

Program Data Vector

During the second iteration of the nested DO loop, the value of Month2, referenced by m (i,j), is added to Qtr1. 
     data finance.quarters(drop=i j);
        set finance.monthly;
        array m(4,3) month1-month12;
        array Qtr(4);
        do i=1 to 4;          i=1
          qtr(i=0);
         > do j=1 to 3;       j=2
              qtr(1)+m(1,2);
           end;
        end;
     run;

Program Data Vector

The nested DO loop continues to execute until the index variable j exceeds the stop value, 3. When the nested DO loop completes execution, the total sales for the first quarter, Qtr1, has been computed. 
     data finance.quarters(drop=i j);
        set finance.monthly;
        array m(4,3) month1-month12;
        array Qtr(4);
        do i=1 to 4;          i=1
          qtr(i=0);
         > do j=1 to 3;       j=3
              qtr(1)+m(1,3);
           end;
        end;
     run;

Program Data Vector

The outer DO loop increments to 2 and the process continues for the array element Qtr2 and the m array elements Month4 through Month6. 
     data finance.quarters(drop=i j);
        set finance.monthly;
        array m(4,3) month1-month12;
        array Qtr(4);
      > do i=1 to 4;          i=2
          qtr(i=0);
           do j=1 to 3;       j=1
              qtr(i)+m(i,j);
           end;
        end;
     run;

Program Data Vector

After the outer DO loop completes execution, the end of the DATA step is reached and the variable values for the first observation are written to the data set Finance.Quarters. 
     data finance.quarters(drop=i j);
        set finance.monthly;
        array m(4,3) month1-month12;
        array Qtr(4);
      > do i=1 to 4;          i=5 (loop ends)
          qtr(i=0);
           do j=1 to 3;
              qtr(i)+m(i,j);
           end;
        end;
     run;

Program Data Vector

What you have seen so far represents the first iteration of the DATA step. All observations in the data set Finance.Monthly are processed in the same manner. Below is a portion of the resulting data set, which contains the sales figures grouped by quarters.


SAS Data Set Finance.Quarters (Partial Listing)
Year Qtr1 Qtr2 Qtr3 Qtr4
1989 69100 64400 69200 71800
1990 73100 72000 83200 82800
1991 73400 81800 85200 87800



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