diff src/app/spectrogram/MatrixUtils.ts @ 343:8bfd9586c78a

Move some functions out of waveform and into appropriately named modules.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/app/spectrogram/MatrixUtils.ts	Tue May 23 10:41:36 2017 +0100
@@ -0,0 +1,39 @@
+/**
+ * Created by lucast on 23/05/2017.
+ */
+
+export function estimatePercentile(matrix, percentile) {
+  // our sample is not evenly distributed across the whole data set:
+  // it is guaranteed to include at least one sample from every
+  // column, and could sample some values more than once. But it
+  // should be good enough in most cases (todo: show this)
+  if (matrix.length === 0) {
+    return 0.0;
+  }
+  const w = matrix.length;
+  const h = matrix[0].length;
+  const n = w * h;
+  const m = (n > 50000 ? 50000 : n); // should base that on the %ile
+  let m_per = Math.floor(m / w);
+  if (m_per < 1) {
+    m_per = 1;
+  }
+
+  const sample = [];
+  for (let x = 0; x < w; ++x) {
+    for (let i = 0; i < m_per; ++i) {
+      const y = Math.floor(Math.random() * h);
+      const value = matrix[x][y];
+      if (!isNaN(value) && value !== Infinity) {
+        sample.push(value);
+      }
+    }
+  }
+  if (sample.length === 0) {
+    return 0.0;
+  }
+  sample.sort((a, b) => { return a - b; });
+  const ix = Math.floor((sample.length * percentile) / 100);
+  const estimate = sample[ix];
+  return estimate;
+}