tisonkun commented on code in PR #71:
URL: https://github.com/apache/datasketches-rust/pull/71#discussion_r2700729507
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datasketches/src/countmin/sketch.rs:
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@@ -180,6 +180,51 @@ impl CountMinSketch {
}
}
+ /// Divides every counter by two, truncating toward zero.
+ ///
+ /// Useful for exponential decay where counts represent recent activity.
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// # use datasketches::countmin::CountMinSketch;
+ /// let mut sketch = CountMinSketch::new(4, 128);
+ /// sketch.update_with_weight("apple", 3);
+ /// sketch.halve();
+ /// assert!(sketch.estimate("apple") >= 1);
+ /// ```
+ pub fn halve(&mut self) {
+ self.counts.iter_mut().for_each(|c| *c /= 2);
+ self.total_weight /= 2;
+ }
+
+ /// Multiplies every counter by `decay` and truncates back into `i64`.
+ ///
+ /// Values are truncated toward zero after multiplication; choose `decay`
in `(0, 1]`.
+ /// The total weight is scaled by the same factor to keep bounds
consistent.
+ ///
+ /// # Examples
+ ///
+ /// ```rust
+ /// # use datasketches::countmin::CountMinSketch;
+ /// let mut sketch = CountMinSketch::new(4, 128);
+ /// sketch.update_with_weight("apple", 3);
+ /// sketch.decay(0.5);
+ /// assert!(sketch.estimate("apple") >= 1);
Review Comment:
Maybe a more practical example? Ditto `halve`
@mrcroxx how can `halve` and `decay` practically be helpful?
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