I'm trying to create a basic arpeggiator which will randomly generate a tone every 250ms, from one of four octaves of specified notes.

I've managed to get as far as randomly generating any note in that range (with a random 48), but what I'd like to do is allow the user to turn on and off each note (i.e. they could turn on C, E, and G), and have the patch ONLY generate the notes which match C, E, and G.

So, for example, if the user has selected to hear C, E, and G, the [random] object would generate from 0, 1, 2, 3 (for the four octaves of C), leave out 4, 5, 6, 7 (C#), and 8, 9, 10, 11, 12, 13, 14, 15 (D and D#), but include 16, 17, 18, 19, for the four octaves of E.

Obviously, if the [random] object picks a value in what's excluded, it will just not change the value for that 250ms interval.. I'd like it to always select a valid value. The entire process is confusing me somewhat, and hopefully somebody could either suggest a better way to do this, or help figure out this way!

You might be better of splitting this up a bit. First, start with a [random 12] to generate the pitch class. If it selects a note that is not valid, re-bang the [random 12]; otherwise, bang a [random 4] to select the octave, multiply it by 12, and add it to the output of the [random 12]. I'd patch an example for you, but I have like nine beers in me right now. The admin is a little tipsy!

I had a play around with this but got stuck on determining whether or not the note is valid. I think I can work through the rest, but without an if statement or variables, I'm a little lost as to how to ascertain whether or not a 0-12 value is allowed based on whether the user has ticked one of 12 toggle boxes for the 12 notes.

I'm still finding myself struggling with this.. would there be any possibility you could find a few (sober) minutes and cobble something basic together for me? It'd be much appreciated!

Haha, sorry! There are a number of ways to do this. The one I've attached uses a table to keep track of the valid notes. The indices correspond to the pitch. A [random 12] is used to read the table. If the value at that index is 0, then it tries again. Otherwise, it takes the index number and adds it to an octave.

http://www.pdpatchrepo.info/hurleur/randompitch.mmb.pd