Is there something like `Flow lt T gt distinctUntilChanged a

Question

Is there something like `Flow lt T gt distinctUntilChanged areEquivalent old T new T gt Boolean ` but emits the newest of the equivalent values instead of the oldest

Mark · Answer

Use case a search box with live search results I want to capture search history items but of course you don t want to capture an item for each keystroke so if an items is a prefix of the following item then treat that prefix as an equivalent and so ignore it

Adam Powell · Answer

this sounds underspecified Implemented as you described in your first message you have something that is equivalent to having no operator at all emits the newest of the equivalent values simplifies to always emit the latest value i e no operator

stojan · Answer

have you tried `debounce ` instead typically in combination with `mapLatest` that way you ignore keystrokes for a certain time duration That s the pattern I typically use for search with autocomplete

Adam Powell · Answer

and yeah that point up if you ignored any later emission with the same prefix you d never see the more specific search query to run so that s not what you want either

Dominaezzz · Answer

Not quite an answer but for my search boxes instead of using `debounce` I just do `mapLatest` with a delay in it before the actual fetching

Adam Powell · Answer

Yeah the Latest family of functions are great for this sort of thing and unique to flows if you re used to rx

stojan · Answer

gt unique to flows if you re used to rx actually `mapLatest` is similar to `switchMap switchMapSingle` depending on plain on suspend function

jw · Answer

Yeah in Rx you would do switchMap with a delay on the inner observable Latest in Flow is switch in Rx

Mark · Answer

Thanks all In my case I already use `debounce` however it s not enough because there is no value that can adequately distinguish between a slow typer this is an east asian language learning app where the learner could legitimately take many seconds to type a character and someone who is looking up a word seeing the results and quickly moving on Debounce works well when the user is typing fast or backspacing the search text to oblivion So I need some best effort logic that will discard search text that is clearly a stepping stone to what the user is actually aiming for though this logic is beyond the scope here Regarding the part about never emitting the final value my initial thought was that s okay because as soon as the user clears the search box then it s emitted and that leaving the app `onPause` could act as a trigger to flush the current search text However that latter part sounds messy and makes me lean towards placing the discarding logic in the data source where it would potentially replace the latest history item instead of just adding

Chris Fillmore · Answer

In case this is useful to you fyi there is a `debounce` overload which accepts a lambda ` T gt Long` where you can set the debounce value dynamically based on the value emitted <https kotlinlang org api kotlinx coroutines kotlinx coroutines core kotlinx coroutines flow debounce html>

Mark · Answer

Thanks < Chris Fillmore> although I already use this