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Graphics Examples

An Introductory Graph

Suppose that you have data for ACME Corporation's stock price and you want a simple PRICE × DAY graph to see the overall trend of the stock's price. The data are as follows.

Day   Price
0 43.75
5 48.00
10 59.75
15 75.5
20 59.75
25 71.50
30 70.575
35 61.125
40 79.50
45 72.375
50 67.00
55 54.125
60 58.750
65 43.625
70 47.125
75 45.50

To graph a scatter plot of these points, enter the following statements. These statements generate Figure 12.1.

   proc iml;                            /* invoke IML        */
      call gstart;                      /* start graphics    */
      xbox={0 100 100 0};
      ybox={0 0 100 100};
      day=do(0,75,5);                   /* initialize day    */
      price={43.75,48,59.75,75.5,       /* initialize price  */
          59.75,71.5,70.575,
          61.125,79.5,72.375,67,
          54.125,58.75,43.625,
          47.125,45.50};
      call gopen;                       /* start new graph   */
      call gpoly(xbox,ybox);       /* draw a box around plot */
      call gpoint(day,price);           /* plot the points   */
      call gshow;                       /* display the graph */

inex12o1.gif (1661 bytes)

Figure 12.1: Scatter plot

Note that the GSTART statement initializes the graphics session. It usually needs to be called only once. Next, you enter the data matrices. Then you open a graphics segment (that is, begin a new graph) with the GOPEN command. The GPOINT command draws the scatter plot of points of DAY versus PRICE. The GSHOW command displays the graph.

Notice also that, for this example, the x coordinate of the data is DAY and that 0 \leq {DAY} \leq 100.The y coordinate is PRICE, which ranges from 0 \leq {PRICE} \leq 100. For this example, the ranges are this way because the IML default ranges are from 0 to 100 on both the x and y axes. Later on you learn how to change the default ranges for the axes with the GWINDOW statement so that you can handle data with any range of values.

Of course, this graph is quite simple. By the end of this chapter, you will know how to add axes and titles, to scale axes, and to connect the points with lines.

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