# IBM Visualization Data Explorer Programmer's Reference

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# Chapter 5. Working with Data

Partial Table-of-Contents

- 5.1 Add Module Example--Add a Number to Every Data Value
- 5.2 Add2 Module Example--Add Two Data Fields
- 5.3 Add2Invalid Module Example--Manipulate Invalid Data

  For modules that manipulate the data component of an Object, positions and connections are often irrelevant. The Statistics module, for example, computes the mean of a data Field regardless of whether the connections are quads or cubes. In fact, it is unnecessary for the Statistics module to examine or access the connections component at all.

  The Module Builder is well suited to creating such modules.

  ## 5.1 Add Module Example--Add a Number to Every Data Value

  The Add module adds a number to every data value in a Field.

  Note: | This example is for illustration rather than "practice," since its function is already provided by Compute (see Compute in IBM Visualization Data Explorer User's Reference).

  The Add module takes two inputs: the first, `data`, is of type `field` and has no default value; the second, `addend`, is of type `scalar`, and has a default value of zero (0).

  The Add module has one output: `result`, of type `field`.

  (1) Start the Module Builder with the command:

        dx -builder

  The Module Builder dialog box appears. Note that the dialog box carries no information, since no module has been specified. (For a simple example of creating a module with the Module Builder, see 3.3 , "Using the Module Builder: A Quick Walk Through")

  (2) Select `Open` from the `File` pull-down menu. An `Open a Module Builder file...` dialog box appears.

  (3) Read in `/usr/local/dx/samples/program_guide/add.mb` as follows:

  - Type the full path name in the `Filter` field of the dialog box.
  - Click on (in sequence):
    - the `Filter` button
    - the name of the file in the `Files` field
    - the `OK` button.
    Information describing the inputs and output of the module (extracted from the `add.mb` file) appears in the Module Builder dialog box. (Of course, if you were creating this module from scratch, you would fill in the information yourself.)

  (4) Save the .mb file to a writable directory (use `Save As...` in the `File` pull-down menu).

  (5) Select `Create All` from the `Build` pull-down menu of the dialog box. This option creates three files for the module: `add.c`, `add.mdf`, and `add.make`.

  (6) Implement the Add function.

  Use an editor to add the following lines after "User's code goes here," near the end of the `add.c` file:

         int i;
         float value;
         /* first implement the default for addend of 0 */
         if (addend_knt == 0)
            value = 0;
         else
            value = *addend_data;
         /* add addend to each value in the data field */
         for (i=0; i < result_knt; i++) {
            result_data[i] = data_data[i] + value;
         }
         return 1;

  The file `/usr/local/dx/samples/program_guide/add.c` contains a completed version of this program.

  (7) To create a version of Data Explorer that includes the Add module, enter the command:

      make -f add.make dxexec

  (You have now created an executable that contains the Add module.)

  (8) To invoke this version, enter:

      dx  -mdf ./add.mdf -exec ./dxexec

  This command starts Data Explorer (the `add.mdf` file tells the graphical user interface about Add and its inputs and outputs). The executable dxexec invoked here is the one created in Step 6.

  (9) With this version of Data Explorer you can now run any visual program that uses the Add module. One such program is `/usr/local/dx/samples/program_guide/add.net`

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