Hi, how can I phrase this code so I don't have three identical `ResultsChips` for each headline? I u...

# getting-started

[Nat Strangerweather]

Hi, how can I phrase this code so I don't have three identical ResultsChips for each headline? I understand why I am getting this result (because of the loops), but I have no idea how to resolve it. 🧵

[Nat Strangerweather]

val dateTimeFormatter: DateTimeFormatter =
                    DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss O yyyy")

                items(newsFeeds?.sortedByDescending {item->
                    LocalDateTime.parse(item.feedItem.pubDate, dateTimeFormatter)
                }?.filter { it.feedTitle == title } ?: emptyList()) { item ->
                    ResultsChip(item.id, item.feedItem.title, navController)
                }

[Joffrey]

I think we're missing a bunch of context here, I'm not sure how to help right now. What loops are you talking about? What does the list that you pass to items() look like (once sorted and filtered)?

Also, what's the difference between item.feedTitle and item.feedItem.title? If they are the same, what would you expect to look different in the ResultsChip?

[Joffrey]

Also, is that a JetPack Compose list? (because that's also unclear to me at first glance, I'm not familiar with it, and this is not the #compose-android channel, so it's not a default context)

[Nat Strangerweather]

Hi, well by loops I mean the fact that I have item-> twice. Yes, it's a Compose list.

[Nat Strangerweather]

Ok, I'll ask them!

[Nat Strangerweather]

😊

[Joffrey]

Oh I'm not saying your post doesn't belong here, I'm just saying the channel gives context. But in #getting-started you should assume we don't have any context 🙂

[Nat Strangerweather]

I asked here because I am trying to order my list according to its publication date.

[Nat Strangerweather]

Until I add the sorting code, all works fine.

[Nat Strangerweather]

The original code is this:

items(newsFeeds?.filter { it.feedTitle == title } ?: emptyList()) { item ->
                    ResultsChip(item.id, item.feedItem.title, navController)
                }

[Nat Strangerweather]

Shall I ask the other channel?

[Joffrey]

Not necessarily, as the problem might not come from the Compose list itself. I think you should extract the list to a variable rather than putting the whole expression in the items() parameter. It will be a bit clearer and will also allow to print the list for debugging, or put a breakpoint more easily. What does the list look like before and after sorting? What about after filtering?

[Joffrey]

By the way, this is unrelated, but note that if you filter the list, there is no real point in sorting the whole list, so it is better to filter first, and then sort.

[Nat Strangerweather]

The list is fetched online and stored into a room database. It is then observed from there. It has a number of attributes like: title, date, link...

[Nat Strangerweather]

What I want is for the titles to appear in the order that they are published, latest first.

[Joffrey]

Sorry I wasn't clear, I meant what is the list exactly? What values do you see for the input list when you witness the behaviour of ResultsChip you're describing? (what titles, what dates, what's the size of the list, before filtering, after filtering, this kind of things). Did you look at this when debugging?

[Joffrey]

Probably you see duplicates because you have duplicates in the input data.

Until I add the sorting code, all works fine

Does it work fine again when you remove the sorting code and go back to just filtering? Are you sure the dupicates are not just farther apart, and you just don't notice them?

[Nat Strangerweather]

No, there are no duplicates, I am sure of that. This is what my room database looks like.

[Nat Strangerweather]

At this stage all I need is to show the headline/title on a chip.

[Nat Strangerweather]

which is working well, but I wanted them ordered

[Joffrey]

This is what my room database looks like

That is just a tiny extract, though. Or does the whole table only contain items 55-64?

[Nat Strangerweather]

yeah

[Nat Strangerweather]

I'll try a better answer

[Nat Strangerweather]

The lists vary in size depending on which rss feed is being downloaded. Some of them only have a few headlines and others have 200, like the Guardian.

[Joffrey]

I mean, sortingByDescending cannot add elements to the list, so if you see duplicates eventually, they must have been there originally. Sorting does bring duplicates next to each other, making the duplication more obvious in long lists. So I believe if you see duplicate chips, and you want to be sure there are no duplicates in DB, you should run a query with the duplicate title from the chips and see how many results you find in DB

[Nat Strangerweather]

But then why would there be three identical chips for every single headline on every newspaper?

[Joffrey]

Because maybe you did 3 tests, and inserted 3 times the same RSS feeds in your DB without unique constraints?

[Nat Strangerweather]

That makes sense

[Nat Strangerweather]

I will analyse the database

[Nat Strangerweather]

thanks!

[Joffrey]

No problem

[Nat Strangerweather]

Yes, you were spot on!

[Joffrey]

Nice, I'm glad you found the issue! ☺️

[Joffrey]

Now if you want to prevent duplication you should probably add some logic during insertion to filter out duplicates (for instance based on the last known post date for a given feed), and maybe add a unicity constraint in the DB on some set of columns to fail in case of duplicate insertion so the problem is prevented at the root

[Nat Strangerweather]

Yes, sounds like a good plan of action.

[xoangon]

Despite this not being a Compose-related Slack channel, I’ve seen your example and I do wanted to point out two concerns:
• You should perform collection operations inside remember blocks for performance reasons
• If you’re using DB models in Compose, those may all be unstable and lead to a whole lot of recompositions on scrolling
If you want more information on this, we can continue this topic by DM

[Nat Strangerweather]

Thank you so much. Will get in touch by DM after the weekend. 🙂