Running models : Working with visualization tools : Data logger

The Data Logger tool does not display model data, but records it in files for later analysis with statistical tools. There are other ways of doing this:

• The Table Helper can save its contents as a .csv file, but has poor performance with large data sets
• The Snapshot tool can record values as the model runs, but only handles one variable, and needs setting up every time the model is run

By contrast, the Data Logger can handle any size of data set that is usable within Simile, and can log multiple variables, either in separate files or as columns in a single file. Since it is a standard helper, many instances can be added for different groups of values, and the setup can be saved as part of a general helper layout.

Using the tool

The tool's canvas will be blank when it is first added. To log a variable, hit the + button and click the variable on the model diagram. It will be listed within its hierarchy of submodels, with a '-' button ffor its removal. Hit + again to add more variables. The rightmost button in the helper's toolbar switches between saving separate files for each variable (named by the variable's caption) and a single file (log.csv) with each variable in its own column.

Saved file format

The helper will not save any data until you select a folder in which to save it. Click the toolbar button with the folder icon and navigate to the desired location. Now a line is written to the log file(s) at each display point as the model executes. The files are in .csv format with the time points stored in the left hand column. If the values being saved are arrays, they will be written as series of alternating indices and values, with each series enclosed in curly brackets, i.e., the same format as data popups or directly-entered file parameters.

The file is closed when the model is paused, and opened for appending more data when it is restarted. When the model is first run after a reset or rebuild, the file will be opened for writing, so the previous contents will be overwritten unless they have been moved.

As of Simile v6.9, it is also possible to log model data to a database -- either a file in some Excel-compatible format (.xls, .xlsx etc) or a MySQL database. To log to a database file, simply select it from the file dialogue. To log to a MySQL database, cancel the file dialogue and this will cause the database specification dialogue to appear. Here you enter the hostname, username, password and name of the MySQL database.

When logging to a database, each component being logged will have values put in its own column in the database. If logging an array component, there will be a separate column for each element in the array, named value/n where value is the name of the component and n is the index of the element. (value/n1/n2/... for multi-dimensional arrays). The values will be written to a table called 'Run 0' until the model is reset, after which new tables called 'Run 1', 'Run 2' etc will be created for data values from subsequent runs.