Bar graph added.

node_modules/vega-statistics/src/regression/exp.js

@@ -0,0 +1,29 @@
+import ols from './ols';
+import {points, visitPoints} from './points';
+import rSquared from './r-squared';
+
+export default function(data, x, y) {
+  // eslint-disable-next-line no-unused-vars
+  const [xv, yv, ux, uy] = points(data, x, y);
+  let YL = 0, XY = 0, XYL = 0, X2Y = 0, n = 0, dx, ly, xy;
+
+  visitPoints(data, x, y, (_, dy) => {
+    dx = xv[n++];
+    ly = Math.log(dy);
+    xy = dx * dy;
+
+    YL += (dy * ly - YL) / n;
+    XY += (xy - XY) / n;
+    XYL += (xy * ly - XYL) / n;
+    X2Y += (dx * xy - X2Y) / n;
+  });
+
+  const [c0, c1] = ols(XY / uy, YL / uy, XYL / uy, X2Y / uy),
+        predict = x => Math.exp(c0 + c1 * (x - ux));
+
+  return {
+    coef: [Math.exp(c0 - c1 * ux), c1],
+    predict: predict,
+    rSquared: rSquared(data, x, y, uy, predict)
+  };
+}