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use super::stateless_op::StatelessOp;
use crate::channels::operator_io::Output;
use crate::stream::StreamBuilder;
use crate::types::{Data, DataMessage, MaybeKey, Message, Timestamp};
/// Flatten a stream of iterables by emitting each element of every iterable as a distinct message.
pub trait Flatten<K, VI, T, VO, I>: super::sealed::Sealed {
/// Flatten a datastream. Given a stream of some iterables, this function consumes
/// each iterable and emits each of its elements downstream.
///
/// # Key and Time
/// If the message containing the iterator has a key or timestamp,
/// they are cloned and attached to every emitted message.
///
/// # Example
///
/// Only retain numbers <= 42
/// ```rust
/// use malstrom::operators::*;
/// use malstrom::runtime::SingleThreadRuntime;
/// use malstrom::snapshot::NoPersistence;
/// use malstrom::sources::{SingleIteratorSource, StatelessSource};
/// use malstrom::worker::StreamProvider;
/// use malstrom::sinks::{VecSink, StatelessSink};
///
/// let sink = VecSink::new();
/// let sink_clone = sink.clone();
///
/// SingleThreadRuntime::builder()
/// .persistence(NoPersistence)
/// .build(move |provider: &mut dyn StreamProvider| {
/// provider.new_stream()
/// .source("numbers", StatelessSource::new(
/// SingleIteratorSource::new([vec![1, 2, 3], vec![4, 5], vec![6]])
/// ))
/// .flatten("flatten")
/// .sink("sink", StatelessSink::new(sink_clone));
/// })
/// .execute()
/// .unwrap();
///
/// let expected: Vec<i32> = vec![1, 2, 3, 4, 5, 6];
/// let out: Vec<i32> = sink.into_iter().map(|x| x.value).collect();
/// assert_eq!(out, expected);
/// ```
fn flatten(self, name: &str) -> StreamBuilder<K, VO, T>;
}
impl<K, VI, T, VO, I> Flatten<K, VI, T, VO, I> for StreamBuilder<K, VI, T>
where
K: MaybeKey,
I: Iterator<Item = VO>,
VI: IntoIterator<Item = VO, IntoIter = I> + Data,
VO: Data,
T: Timestamp,
{
fn flatten(self, name: &str) -> StreamBuilder<K, VO, T> {
self.stateless_op(
name,
move |item: DataMessage<K, VI, T>, out: &mut Output<K, VO, T>| {
let key = item.key;
let timestamp = item.timestamp;
for x in item.value {
out.send(Message::Data(DataMessage::new(
key.clone(),
x,
timestamp.clone(),
)))
}
},
)
}
}
#[cfg(test)]
mod tests {
use itertools::Itertools;
use crate::{
operators::*,
sinks::StatelessSink,
sources::{SingleIteratorSource, StatelessSource},
testing::{get_test_rt, VecSink},
};
#[test]
fn test_flatten() {
let collector = VecSink::new();
let rt = get_test_rt(|provider| {
provider
.new_stream()
.source(
"source",
StatelessSource::new(SingleIteratorSource::new([
vec![1, 2],
vec![3, 4],
vec![5],
])),
)
.flatten("flatten")
.sink("sink", StatelessSink::new(collector.clone()));
});
rt.execute().unwrap();
let result = collector.into_iter().map(|x| x.value).collect_vec();
let expected = vec![1, 2, 3, 4, 5];
assert_eq!(result, expected);
}
/// check we preserve the timestamp on every message
#[test]
fn test_preserves_time() {
let collector = VecSink::new();
let rt = get_test_rt(|provider| {
provider
.new_stream()
.source(
"source",
StatelessSource::new(SingleIteratorSource::new([
vec![1, 2],
vec![3, 4],
vec![5],
])),
)
.flatten("flatten")
.sink("sink", StatelessSink::new(collector.clone()));
});
rt.execute().unwrap();
let expected = vec![(1, 0), (2, 0), (3, 1), (4, 1), (5, 2)];
let result = collector
.into_iter()
.map(|x| (x.value, x.timestamp))
.collect_vec();
assert_eq!(result, expected);
}
// check we preserve the key
#[test]
fn test_preserves_key() {
let collector = VecSink::new();
let rt = get_test_rt(|provider| {
provider
.new_stream()
.source(
"source",
StatelessSource::new(SingleIteratorSource::new([
vec![1, 2],
vec![3, 4, 5],
vec![6],
])),
)
.key_local("key-local", |x| x.value.len())
.flatten("flatten")
.sink("sink", StatelessSink::new(collector.clone()));
});
rt.execute().unwrap();
let expected = vec![(1, 2), (2, 2), (3, 3), (4, 3), (5, 3), (6, 1)];
let result = collector
.into_iter()
.map(|d| (d.value, d.key))
.collect_vec();
assert_eq!(result, expected);
}
}