add rarity.py

Author: nicola-corbellini

pyeyesweb/analysis_primitives/rarity.py

@@ -0,0 +1,42 @@
+import numpy as np
+
+from pyeyesweb.data_models.sliding_window import SlidingWindow
+
+
+class Rarity:
+
+    def __call__(self, sliding_window: SlidingWindow, alpha: float = 0.5) -> float:
+        if not sliding_window.is_full():
+            return np.nan
+
+        samples, _ = sliding_window.to_array()
+        n_samples = len(samples)
+
+        # Number of bins
+        n_bins = int(np.sqrt(n_samples))
+        n_bins = max(n_bins, 1)
+        print(f"Using {n_bins} for {n_samples} samples.")
+
+        # Histogram
+        counts, bin_edges = np.histogram(samples, bins=n_bins)
+
+        # Convert to probability distribution
+        probabilities = counts / n_samples
+
+        # Most probable bin
+        most_probable_bin_index = np.argmax(probabilities)
+        most_probable_p = probabilities[most_probable_bin_index]
+
+        # Current sample bin
+        last_sample = samples[-1]
+        last_sample_bin_index = np.searchsorted(bin_edges, last_sample, side='right') - 1
+        last_sample_bin_index = np.clip(last_sample_bin_index, 0, n_bins - 1)
+        last_sample_p = probabilities[last_sample_bin_index]
+
+        # Compute rarity using probabilities
+        d1 = abs(most_probable_bin_index - last_sample_bin_index)  # distance in bin space
+        d2 = most_probable_p - last_sample_p  # probability difference
+
+        rarity = d1 * d2 * alpha
+        return float(rarity)
+