implement freeze check

src/lib.rs

@@ -36,8 +36,8 @@ use thiserror::Error;
 
 mod qc_tests;
 pub use qc_tests::{
-    buddy_check::buddy_check, dip_check::dip_check, range_check::range_check, sct::sct,
-    step_check::step_check,
+    buddy_check::buddy_check, dip_check::dip_check, freeze_check::freeze_check,
+    range_check::range_check, sct::sct, step_check::step_check,
 };
 
 mod util;

src/qc_tests/freeze_check.rs

@@ -0,0 +1,45 @@
+use crate::{Error, Flag, SeriesCache};
+
+/// Timeseries QC test that checks for streaks of repeating values.
+///
+/// If `num_points` observations in a row are identical, the last will be flagged as Flag::Fail, if
+/// any of the last `num_points` observations are missing, it will be flagged as Flag::DataMissing,
+/// else Flag::Pass.
+///
+/// As (`num_points` - 1) predecessors to each observation are needed, the [`SeriesCache`] provided must have
+/// `num_leading_points` >= `num_points` - 1.
+///
+/// ## Errors
+///
+/// - data is invalid
+/// - data has `num_leading_points` < `num_points` - 1
+pub fn freeze_check(data: &SeriesCache, num_points: u8) -> Result<Vec<Flag>, Error> {
+    let (leading_trim, lead_overflow) = data
+        .num_leading_points
+        .overflowing_sub(num_points.saturating_sub(1));
+
+    if lead_overflow || (leading_trim + num_points) as usize > data.values.len() {
+        // TODO: nicer error here?
+        return Err(Error::InvalidInputShape("data".to_string()));
+    }
+
+    let trimmed = &data.values
+        [leading_trim as usize..(data.values.len() - data.num_trailing_points as usize)];
+
+    let windows = trimmed.windows(num_points as usize);
+
+    Ok(windows
+        .map(|data| {
+            if data.contains(&None) {
+                return Flag::DataMissing;
+            }
+            let data: Vec<f32> = data.iter().map(|opt| opt.unwrap()).collect();
+
+            let base = data[0];
+            if !data.iter().any(|x| *x != base) {
+                return Flag::Fail;
+            }
+            Flag::Pass
+        })
+        .collect())
+}

src/qc_tests/mod.rs

@@ -1,5 +1,6 @@
 pub(super) mod buddy_check;
 pub(super) mod dip_check;
+pub(super) mod freeze_check;
 pub(super) mod range_check;
 pub(super) mod sct;
 pub(super) mod step_check;