tisonkun commented on code in PR #59:
URL: https://github.com/apache/datasketches-rust/pull/59#discussion_r2660026906
##########
datasketches/src/theta/sketch.rs:
##########
@@ -116,6 +118,89 @@ impl ThetaSketch {
pub fn iter(&self) -> impl Iterator<Item = u64> + '_ {
self.table.iter()
}
+
+ /// Returns the approximate lower error bound given the specified number
of Standard Deviations.
+ ///
+ /// # Arguments
+ ///
+ /// * `num_std_devs` - The number of standard deviations from the mean for
the tail bounds. Must
+ /// be 1, 2, or 3, corresponding to approximately 67%, 95% and 99%
confidence intervals.
+ ///
+ /// # Returns
+ ///
+ /// Returns `Ok(lb)` where `lb` is the approximate lower bound value.
+ ///
+ /// # Errors
+ ///
+ /// Returns an error if `num_std_devs` is not 1, 2, or 3.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use datasketches::theta::ThetaSketch;
+ ///
+ /// let mut sketch = ThetaSketch::builder().lg_k(12).build();
+ /// for i in 0..10000 {
+ /// sketch.update(i);
+ /// }
+ ///
+ /// let estimate = sketch.estimate();
+ /// let lower_bound = sketch.lower_bound(2).unwrap();
+ /// let upper_bound = sketch.upper_bound(2).unwrap();
+ ///
+ /// assert!(lower_bound <= estimate);
+ /// assert!(estimate <= upper_bound);
+ /// ```
+ pub fn lower_bound(&self, num_std_devs: u32) -> Result<f64, Error> {
+ if !self.is_estimation_mode() {
+ return Ok(self.num_retained() as f64);
+ }
+ binomial_bounds::lower_bound(self.num_retained() as u64, self.theta(),
num_std_devs)
+ }
Review Comment:
We already have a `NumStdDev` enum:
https://github.com/apache/datasketches-rust/blob/9ade42d639afd013d19c3454a14773b6d54edc25/datasketches/src/hll/estimator.rs#L327-L341
You can reuse it by moving the struct to a shared module level and thus we
would never error here.
Besides, we may consider where to place these shared structs, including the
`ResizeFactor`. `datasketches::{NumStdDev, ResizeFactor}` is fair enough now,
but perhaps pollute the top-level namespace too much.
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