1 files changed, 53 insertions, 0 deletions
diff --git a/app/bits/assets/trendline.js b/app/bits/assets/trendline.js
new file mode 100755
index 0000000..48e2522
--- /dev/null
+++ b/app/bits/assets/trendline.js
@@ -0,0 +1,53 @@
+function getAvg(arr) {
+    const total = arr.reduce((acc, c) => acc + c, 0);
+    return total / arr.length;
+}
+
+function getSum(arr) {
+    return arr.reduce((acc, c) => acc + c, 0);
+}
+
+function trendline(data, xKey, yKey) {
+    const xData = data.map((value) => value[xKey]);
+    const yData = data.map((value) => value[yKey]);
+
+    // average of X values and Y values
+    const xMean = getAvg(xData);
+    const yMean = getAvg(yData);
+
+    // Subtract X or Y mean from corresponding axis value
+    const xMinusxMean = xData.map((val) => val - xMean);
+    const yMinusyMean = yData.map((val) => val - yMean);
+
+    const xMinusxMeanSq = xMinusxMean.map((val) => Math.pow(val, 2));
+
+    const xy = [];
+    for (let x = 0; x < data.length; x++) {
+        xy.push(xMinusxMean[x] * yMinusyMean[x]);
+    }
+
+    // const xy = xMinusxMean.map((val, index) => val * yMinusyMean[index]);
+
+    const xySum = getSum(xy);
+
+    // b1 is the slope
+    const b1 = xySum / getSum(xMinusxMeanSq);
+    // b0 is the start of the slope on the Y axis
+    const b0 = yMean - b1 * xMean;
+
+    return {
+        slope: b1,
+        yStart: b0,
+        calcY: (x) => b0 + b1 * x,
+    };
+}
+
+const averageDelta = ([x,...xs]) => {
+    if (x === undefined)
+        return NaN
+    else
+        return xs.reduce(
+            ([acc, last], x) => [acc + (x - last), x],
+            [0, x]
+        ) [0] / xs.length
+}
+\ No newline at end of file