feat(transducers): add line(), curve()

packages/transducers/README.md

@@ -955,11 +955,13 @@ tx.transduce(tx.map((x) => x*10), tx.push(), tx.range(4))
 
 - [choices](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/choices.ts)
 - [concat](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/concat.ts)
+- [curve](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/curve.ts)
 - [cycle](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/cycle.ts)
 - [dup](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/dup.ts)
 - [extendSides](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/extend-sides.ts)
 - [iterate](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/iterate.ts)
 - [keys](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/keys.ts)
+- [line](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/line.ts)
 - [normRange](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/norm-range.ts)
 - [padSides](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/pad-sides.ts)
 - [pairs](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/pairs.ts)

packages/transducers/README.tpl.md

@@ -721,11 +721,13 @@ tx.transduce(tx.map((x) => x*10), tx.push(), tx.range(4))
 
 - [choices](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/choices.ts)
 - [concat](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/concat.ts)
+- [curve](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/curve.ts)
 - [cycle](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/cycle.ts)
 - [dup](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/dup.ts)
 - [extendSides](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/extend-sides.ts)
 - [iterate](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/iterate.ts)
 - [keys](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/keys.ts)
+- [line](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/line.ts)
 - [normRange](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/norm-range.ts)
 - [padSides](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/pad-sides.ts)
 - [pairs](https://github.com/thi-ng/umbrella/tree/master/packages/transducers/src/iter/pairs.ts)

packages/transducers/src/index.ts

@@ -109,11 +109,13 @@ export * from "./func/renamer";
 export * from "./iter/as-iterable";
 export * from "./iter/choices";
 export * from "./iter/concat";
+export * from "./iter/curve";
 export * from "./iter/cycle";
 export * from "./iter/dup";
 export * from "./iter/extend-sides";
 export * from "./iter/iterate";
 export * from "./iter/keys";
+export * from "./iter/line";
 export * from "./iter/norm-range";
 export * from "./iter/pad-sides";
 export * from "./iter/palindrome";

packages/transducers/src/iter/curve.ts

@@ -0,0 +1,40 @@
+import { expFactor, fit } from "@thi.ng/math";
+
+/**
+ * Iterator yielding `steps` + 1 interpolated values along an
+ * exponential curve in the closed `[start .. end]` interval. The
+ * curvature can be controlled via `falloff` (default: 1), which is used
+ * as a power of 10 to compute the exponential decay / growth factor.
+ * Use `falloff` < 0 for ease in or > 0 for ease out.
+ *
+ * @example
+ * ```ts
+ * [...curve(50, 100, 10, 2)]
+ * // [
+ * //   50,
+ * //   70.228,
+ * //   82.354,
+ * //   89.624,
+ * //   93.982,
+ * //   96.594,
+ * //   98.160,
+ * //   99.099,
+ * //   99.662,
+ * //   100
+ * // ]
+ * ```
+ *
+ * @param start -
+ * @param end -
+ * @param steps -
+ * @param falloff -
+ */
+export function* curve(start: number, end: number, steps = 10, falloff = 1) {
+    const fe = 1 / 10 ** falloff;
+    const f = expFactor(1, fe, steps - 1);
+    let t = 1;
+    for (; --steps >= 0; ) {
+        yield fit(t, 1, fe, start, end);
+        t *= f;
+    }
+}

packages/transducers/src/iter/line.ts

@@ -0,0 +1,30 @@
+import { map } from "../xform/map";
+import { normRange } from "./norm-range";
+
+/**
+ * Iterator yielding `steps` + 1 interpolate values on a line in the
+ * closed `[start .. end]` interval.
+ *
+ * @remarks
+ * This is similar to {@link range}, but potentially provides more
+ * precise values (by avoiding the accumulation of floating point errors
+ * during iteration).
+ *
+ * @example
+ * ```ts
+ * [...line(50, 100, 10)]
+ * // [
+ * //    50, 55, 60, 65, 70,
+ * //    75, 80, 85, 90, 95,
+ * //   100
+ * // ]
+ * ```
+ *
+ * @param start -
+ * @param end -
+ * @param steps -
+ */
+export const line = (start: number, end: number, steps = 10) => {
+    const delta = end - start;
+    return map((t) => start + delta * t, normRange(steps));
+};