Grapher's Null criteria feature can be used to remove NULL data from the a graph. 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 Home | New Graph command.
- Click on the plot to select it.
- In the Property Manager, click on the Data Limits tab.
- In the Criteria Filter section, change the Criteria to Null.
- Click the Set button.
- In the Criteria dialog, check the box next to the Use NULL criteria option, if needed.
- 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.
- Click OK in the Criteria dialog and the NULL values are removed from the graph.
Two line plots showing the effect of applying a NULL criteria to a graph
Updated September 21, 2018