CODEWITHSUNDEEP
rust
Doe
Doe

Reputation: 675

How can slices be split using another slice as a delimiter?

Does the standard library provide a way to split a slice [T] using another slice of the same type as a delimiter? The library's documentation lists methods that operate on single-element delimiters rather than slices.

For example: A slice of 5 u64 integers [1u64, 4u64, 0u64, 0u64, 8u64] split using [0u64, 0u64] as a delimiter would result in two slices [1u64, 4u64] and [8u64].

Upvotes: 5

Views: 674

Answers (1)

malbarbo
malbarbo

Reputation: 11177

Does the standard library provide a way to split a slice [T] using another slice of the same type as a delimiter?

As of Rust 1.9, no, but you can implement it:

fn main() {
    let a = [1, 4, 7, 0, 0, 8, 10, 0, 0];
    let b = [0, 0];
    let mut iter = split_subsequence(&a, &b);
    assert_eq!(&[1, 4, 7], iter.next().unwrap());
    assert_eq!(&[8, 10], iter.next().unwrap());
    assert!(iter.next().unwrap().is_empty());
    assert_eq!(None, iter.next());
}

pub struct SplitSubsequence<'a, 'b, T: 'a + 'b> {
    slice: &'a [T],
    needle: &'b [T],
    ended: bool,
}

impl<'a, 'b, T: 'a + 'b + PartialEq> Iterator for SplitSubsequence<'a, 'b, T> {
    type Item = &'a [T];

    fn next(&mut self) -> Option<Self::Item> {
        if self.ended {
            None
        } else if self.slice.is_empty() {
            self.ended = true;
            Some(self.slice)
        } else if let Some(p) = self.slice
                                    .windows(self.needle.len())
                                    .position(|w| w == self.needle) {
            let item = &self.slice[..p];
            self.slice = &self.slice[p + self.needle.len()..];
            Some(item)
        } else {
            self.ended = true;
            let item = self.slice;
            self.slice = &self.slice[self.slice.len() - 1..];
            Some(item)
        }
    }
}

fn split_subsequence<'a, 'b, T>(slice: &'a [T], needle: &'b [T]) -> SplitSubsequence<'a, 'b, T>
    where T: 'a + 'b + PartialEq
{
    SplitSubsequence {
        slice: slice,
        needle: needle,
        ended: false,
    }
}

Note that this implementation uses a naive algorithm for finding an equal subsequence.

Upvotes: 4

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