Split slice, keep delimiters

help
1

Hi, I have a problem that would be nicely solved if I could split up a slice and get an iterator over sub-slices, separated by elements that match a certain condition. I.e, exactly like the "split" method on slices, but I need the matching element to be contained in the sub-slices.

More accurately, I don't necessarily need the matching element (the delimiter) to be part of the sub-slices, but I somehow need to connect a particular sub-slice with the preceding delimiter in order to process that sub-slice. Given my original slice, what I ideally would like is something that repeatedly calls a function whose first argument is the delimiter, and the second argument is a slice (or an iterator) containing the following elements up until the next delimiter.

Any ideas how to achieve this nicely? I know I can solve this using nested for loops or similar, but I'm just having fun trying to solve toy problems in the most idiomatic/compact/readable way I can.

2

Here's an interesting approach: playground, though you need to consider what happens in the last iteration.

You can also create your own iterator: playground.

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3

Thanks Alice, I looked at your first suggestion and realised that I forgot to make something clear... The elements of my original slice are enums, and the enum variant I'm splitting on does have an associated data element (i32), i.e:

enum Action {
    BeginShift(u32),
    FallAsleep,
    WakeUp,
}

I want to split with BeginShift as delimiter, and I need to extract it's associated u32 in order to process the following sub-slice. In other words, all delimiters wont be identical, they'll just all be "BeginShift".

I haven't looked at your second suggestion in enough detail yet, but I assume it could be adapted to solve my problem. It would certainly make the "call site" more readable, but since it isn't a standard and documented rust function, I'm not quite sure adding a fair bit of custom iterator code will satisfy the criteria of readability for this particular problem. Still, thanks for the code! I will take a closer look and I'm sure understanding it will help me with other rust problems down the road...

4

The first solution doesn't assume that the delimiter is identical! The delimiter is stored in the delim variable, and can be accessed inside the loop.

5

Looking through your iterator example, it's pretty nice and straightforward... Just need to come up with a good name that makes it fairly obvious at the call site that it's splitting into sub-slices while keeping the delimiters.

6

Also that looks like an advent of code problem :eyes:

7

Hmmm, but there could be multiple delimiters (i.e multiple BeginShift(u32)) in the slice, all with different numbers attached... I don't see how delim could contain more than one.

8

In each iteration of the loop it contains the last one seen. Try running it to see the output.

9

Oh yes, sorry, I see now, the predicate function is updating delim each time it gets called...

Advent of code?? Not sure what that is, I just happen to be stuck in a guarded closet and need to find the best time to escape!

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