By default, Grapher displays all data in the data columns for every plot. Sometimes data is included in the worksheet that should not be plotted. For example, an instrument may record -9999 when the data value cannot be determined. When this happens, the -9999 will appear on the graph. To remove the value and tell Grapher that the value is a NULL value, follow these steps:
- Create the plot as normal by clicking on the appropriate Graphs | Create command.
- Click on the plot to select it. For instance, you might click on the Line/Scatter Plot 1.
- In the Property Manager, click on the Clipping tab.
- Check the box next to the Use criteria option.
- Click the Set button next to the Criteria option. Criteria allow you to tell Grapher which data to plot or which data to exclude.
- To exclude NULL data, check the box next to the Use NULL criteria option.
- If a single NULL value exists in the data set:
- Click the Value button.
- Type the NULL Value, such as -9999 and click OK.
- If a range of NULL values exist in the data set:
- Click the Range button.
- Type the Low and High values. For instance, you might type -999999 for the Low and 0 for the High if all negative values should be ignored. Click OK.
- By default, all used data columns (X, Y, Z columns) in the worksheet are examined to look for the NULL value. If only some of the data columns should be examined or if the NULL information is in another column, uncheck the Data columns only box.
- Click the Select columns button.
- Check the boxes in front of any column that can contain the NULL criteria and click OK.
Set the NULL value in the Criteria dialog to remove points from the line/scatter plot.
- Click OK in the Criteria dialog and the NULL values are removed from the graph.
Updated October 3, 2016