# Working with groups of co-occuring events **URL:** \ **Category:** TidalCycles\ **Tags:** innards\ **Created:** [21 May 2020 19:04 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098 "2020-05-21T19:04:27Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![mattia.paterna](https://uzu.lurk.org/user_avatar/uzu.lurk.org/mattia.paterna/32/112_2.png) [@mattia.paterna](https://uzu.lurk.org/u/mattia.paterna)\ **Post date:** [21 May 2020 19:04 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/1 "2020-05-21T19:04:27Z")
That is exactly what I was looking for, thank you! @yaxu let's assume for a second there is no inversion in Tidal: how would then be possible to make @loopology's function work? ---
**Author:** ![yaxu](https://uzu.lurk.org/user_avatar/uzu.lurk.org/yaxu/32/2_2.png) [@yaxu](https://uzu.lurk.org/u/yaxu)\ **Post date:** [21 May 2020 20:59 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/2 "2020-05-21T20:59:09Z")
Moved to Innards as it's a bit involved.. I'd generalise the type so it works with any number, as in Tidal notes aren't integers but floats. ```haskell inversion :: Num a => Int -> [a] -> [a] inversion _ [] = [] inversion n xs = drop n xs ++ [x + 12 | x <- take n xs] ``` Then I'd get it to with with lists of Tidal events rather than values: ```haskell eventInversion :: Num a => Int -> [Event a] -> [Event a] eventInversion _ [] = [] eventInversion n xs = drop n xs ++ (fmap (fmap (+12)) $ take n xs ) ``` I used fmap to work in the values inside events, and for brevity used fmap on the list too instead of the list comprehension. Then I made this function that allows you to group any co-occuring events and work on them together: ```haskell withFriends :: ([Event a] -> [Event b]) -> Pattern a -> Pattern b withFriends f pat = withEvents munge pat where munge es = concatMap (f) (groupBy (\a b -> whole a == whole b) $ sortOn whole es) ``` Then bring it together: ```haskell invert :: Num b => Int -> Pattern b -> Pattern b invert = withFriends . eventInversion ``` ```haskell d1 $ n (invert 2 "c'maj e'min'4") $ sound "superpiano" ``` ---
**Author:** ![yaxu](https://uzu.lurk.org/user_avatar/uzu.lurk.org/yaxu/32/2_2.png) [@yaxu](https://uzu.lurk.org/u/yaxu)\ **Post date:** [21 May 2020 21:13 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/3 "2020-05-21T21:13:00Z")
It's complicated because tidal patterns are functions from time to events, so you have to make a function that intercepts values on the way out of the pattern, grouping together ones happening at the same time. Here's a less attractive version of `inversion` that works with negative inversions: ```haskell inversion :: Num a => Int -> [Event a] -> [Event a] inversion _ [] = [] inversion n xs = map (\i -> fmap (+ (fromIntegral $ (i `div` l)*12)) (xs !! (i `mod` l))) $ take l [n ..] where l = length xs ``` ---
**Author:** ![mattia.paterna](https://uzu.lurk.org/user_avatar/uzu.lurk.org/mattia.paterna/32/112_2.png) [@mattia.paterna](https://uzu.lurk.org/u/mattia.paterna)\ **Post date:** [21 May 2020 22:05 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/4 "2020-05-21T22:05:55Z")
Thanks for the explanation @yaxu, there are quite many things that I am not able to understand. I will try to summarise them, feel free to skip if you think we are going down the rabbit hole and perhaps it is better to wait. > [@yaxu](#): > > I used fmap to work in the values inside events, and for brevity used fmap on the list too instead of the list comprehension. `fmap` is used here because `Event` is a `Functor` therefore we can't really apply standard functions such as `take` and `+12` right? > [@yaxu](#): > > Then I made this function that allows you to group any co-occuring events and work on them together So here I understand that when we `stack` something as in the case of chords, Tidal creates an `Event` for every single note in the stack and these `Event`s happen to play in the same `Part`, i.e. they are scheduled to be simultaneous? (Plus I got a bit lost inside the function TBH.) ---
**Author:** ![yaxu](https://uzu.lurk.org/user_avatar/uzu.lurk.org/yaxu/32/2_2.png) [@yaxu](https://uzu.lurk.org/u/yaxu)\ **Post date:** [21 May 2020 22:13 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/5 "2020-05-21T22:13:10Z")
> [@mattia.paterna](#): > > `fmap` is used here because `Event` is a `Functor` therefore we can't really apply standard functions such as `take` and `+12` right? Yep! The fmap is there to do something to the value inside the event. > [@mattia.paterna](#): > > So here I understand that when we `stack` something as in the case of chords, Tidal creates an `Event` for every single note in the stack and these `Event` s happen to play in the same `Part` , i.e. they are scheduled to be simultaneous? Yes, so if you played two chords at the same time, this function would treat them as a single chord. At this point tidal isn't creating any events, but composing a function for creating events. > [@mattia.paterna](#): > > (Plus I got a bit lost inside the function TBH.) Yes there's a lot going on here.. ---
**Author:** ![mattia.paterna](https://uzu.lurk.org/user_avatar/uzu.lurk.org/mattia.paterna/32/112_2.png) [@mattia.paterna](https://uzu.lurk.org/u/mattia.paterna)\ **Post date:** [21 May 2020 22:40 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/6 "2020-05-21T22:40:56Z")
> [@yaxu](#): > > Yes there's a lot going on here.. I can see couple of things in there though: - you are using `withEvents`, which (if I am correct) should apply a function to the input pattern - the function that you want to apply is `munge`, which - sorts a list of `Event`s from lowest to highest (I assume with respect of time) based on `whole` (no real idea about it) - groups the resulting list given some predicate (and `whole` is here again) - applies the function coming all the way from `withEvents` and concatenate the result > [@yaxu](#): > > Then bring it together: > > ```haskell > invert :: Num b => Int -> Pattern b -> Pattern b > invert = withFriends . inversion > > ``` but where is `eventInversion` gone? ---
**Author:** ![mattia.paterna](https://uzu.lurk.org/user_avatar/uzu.lurk.org/mattia.paterna/32/112_2.png) [@mattia.paterna](https://uzu.lurk.org/u/mattia.paterna)\ **Post date:** [21 May 2020 22:47 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/7 "2020-05-21T22:47:21Z")
I think this relates to what I was saying somewhere else in the club about the struggle to making things work. What I experience is that I sometimes (hopefully) learn something new in Haskell, e.g. list comprehension. A lot of ideas come on how to tweak this list into that - but then I try to write something and it almost never works because either the function input is not what it should be or the output is not what Tidal wants. ---
**Author:** ![yaxu](https://uzu.lurk.org/user_avatar/uzu.lurk.org/yaxu/32/2_2.png) [@yaxu](https://uzu.lurk.org/u/yaxu)\ **Post date:** [21 May 2020 23:38 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/8 "2020-05-21T23:38:31Z")
Oops that should be - `invert = withFriends . eventInversion` A lot of haskell documentation focuses on working with lazy lists, which isn't often useful with tidal. Generally they're awesome but I'd say that lists are a kind of code smell with tidal. ---
**Author:** ![mattia.paterna](https://uzu.lurk.org/user_avatar/uzu.lurk.org/mattia.paterna/32/112_2.png) [@mattia.paterna](https://uzu.lurk.org/u/mattia.paterna)\ **Post date:** [22 May 2020 03:50 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/9 "2020-05-22T03:50:09Z")
> [@yaxu](#): > > I'd say that lists are a kind of code smell with tidal Definitely interested in knowing more about your point of view. ---
**Author:** ![yaxu](https://uzu.lurk.org/user_avatar/uzu.lurk.org/yaxu/32/2_2.png) [@yaxu](https://uzu.lurk.org/u/yaxu)\ **Post date:** [22 May 2020 10:02 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/10 "2020-05-22T10:02:31Z")
It's just that Tidal paradigm is about functions of time, not data structures like lists.. About defining behaviour and not procedures. ---
**Author:** ![loopology](https://uzu.lurk.org/user_avatar/uzu.lurk.org/loopology/32/60_2.png) [@loopology](https://uzu.lurk.org/u/loopology)\ **Post date:** [22 May 2020 20:42 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/11 "2020-05-22T20:42:55Z")
Thanks a lot for taking the time and energy to explain this, Alex @yaxu. And thanks to Mattia @mattia.paterna for asking. That's going to give me a lot to think about... ---
**Author:** ![mattia.paterna](https://uzu.lurk.org/user_avatar/uzu.lurk.org/mattia.paterna/32/112_2.png) [@mattia.paterna](https://uzu.lurk.org/u/mattia.paterna)\ **Post date:** [23 May 2020 14:53 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/12 "2020-05-23T14:53:00Z")
you're welcome @loopology! I've been trying really hard to get deeper into the innards and every time I see this kind of discussion I jump in straight away. @yaxu I apologise in advance because I'll probably be asking many more times in the next weeks about Tidal paradigm as it is not clear yet to me 🙂 ---
**Author:** ![loopology](https://uzu.lurk.org/user_avatar/uzu.lurk.org/loopology/32/60_2.png) [@loopology](https://uzu.lurk.org/u/loopology)\ **Post date:** [24 May 2020 16:37 UTC](https://uzu.lurk.org/t/working-with-groups-of-co-occuring-events/1098/13 "2020-05-24T16:37:06Z")
@mattia.paterna, please tag me when you do, as I'm on the same track, even if behind you 🙂