[Tutorial] Loops, in Reactions, start numbering at 0

Hello everyone,

Here’s a little tutorial about something that caused people some headaches in the past.

Something to be aware of when setting up mappings is the way the numbering of tracks, devices, parameters, … works.

The numbering in the more common Mappings that have been set up by the devs (like Track Volume, Select Device, etc…) differs a bit from how numbering is handled inside a Reaction Mapping. I think that’s because the common Mappings were set up to be more user-friendly while Reaction Mappings follow the rules set up by the Python language on which the software is built.

This difference is important to keep in mind when you want to store numbers from a Reaction Mapping (for example, a number gotten from Looping through Tracks) inside a Modifier for use inside one of the common Mappings.

Numbering in common Mappings

In common Mappings, the numbering has been set up to start at the number 1.

This means that, for example, Track Number 1 refers to the first Track in your Song.

Numbering in Reaction Mappings

In the Python language, numbering/indexing starts at the number 0. For example, the first item in a list has the index 0, the second item in the list has index 1, etc…
Reaction Mappings also handle numbers this way. When you loop through Tracks, you’re essentially looping through a Python list object.

In the following example I have a Set with 2 Tracks. Using a Reaction I Loop through the Tracks and Log the loop_number accompanied by the name of the Track this number is referring to.

I used a custom made Log function here, it takes 2 arguments:

1. loop_number
2. self.song().tracks[loop_number].name = the Track’s name at the position of that loop_number

It will output as loop_number >> track_name. Following image shows the output in the Log.

How to use a loop_number inside a common Mapping?

If you’re wondering how you can store a loop_number inside a Modifier to use it in one of the common Mappings, then the answer is simply to add 1 to the loop_number.

First, start by setting up an action to store the loop_number inside a Modifier. But before clicking Save, click on the button with the angled brackets, < >. This will let you customize the code.

In the new window, type + 1 next to the loop_number and Save.

In this example, the number at Modifier m1 can now be used to refer to the correct Track Number inside a common Mapping.

Hope this helps.