diff --git a/README.md b/README.md index 1bcab860..3e186188 100644 --- a/README.md +++ b/README.md @@ -652,7 +652,7 @@ Returns a new interval [*niceStart*, *niceStop*] covering the given interval [*s # d3.range([start, ]stop[, step]) · [Source](https://github.com/d3/d3-array/blob/main/src/range.js), [Examples](https://observablehq.com/@d3/d3-range) -Returns an array containing an arithmetic progression, similar to the Python built-in [range](http://docs.python.org/library/functions.html#range). This method is often used to iterate over a sequence of uniformly-spaced numeric values, such as the indexes of an array or the ticks of a linear scale. (See also [d3.ticks](#ticks) for nicely-rounded values.) +Returns an array containing an arithmetic progression, similar to the Python built-in [range](http://docs.python.org/library/functions.html#range). This method is often used to iterate over a sequence of uniformly-spaced numeric values, such as the indexes of an array or the ticks of a linear scale. (See also [d3.ticks](#ticks) for nicely-rounded values, and [d3.linspace](#linspace) if you prefer to specify the number of values rather than the step.) If *step* is omitted, it defaults to 1. If *start* is omitted, it defaults to 0. The *stop* value is exclusive; it is not included in the result. If *step* is positive, the last element is the largest *start* + *i* \* *step* less than *stop*; if *step* is negative, the last element is the smallest *start* + *i* \* *step* greater than *stop*. If the returned array would contain an infinite number of values, an empty range is returned. @@ -671,6 +671,15 @@ d3.range(0, 1, 1 / 49); // BAD: returns 50 elements! d3.range(49).map(function(d) { return d / 49; }); // GOOD: returns 49 elements. ``` +# d3.linspace(start, stop[, n][, endpoint]) · [Source](https://github.com/d3/d3-array/blob/main/src/linspace.js) + +Returns an array containing an arithmetic progression of *n* values ranging from *start* to *end*, including *end* if *endpoint* is requested. Similar to numpy’s [linspace](https://numpy.org/doc/stable/reference/generated/numpy.linspace.html). Defaults to *n* = 50 and *endpoint* = true. + +```js +d3.linspace(0, 1, 101); // [0, 0.01, 0.02, …, 0.99, 1] +d3.linspace(1, 0, 10, false); // [1, 0.9, 0.8, …, 0.1] +``` + # d3.transpose(matrix) · [Source](https://github.com/d3/d3-array/blob/main/src/transpose.js), [Examples](https://observablehq.com/@d3/d3-transpose) Uses the [zip](#zip) operator as a two-dimensional [matrix transpose](http://en.wikipedia.org/wiki/Transpose). diff --git a/src/index.js b/src/index.js index 5fb58e8b..1fb064f6 100644 --- a/src/index.js +++ b/src/index.js @@ -29,6 +29,7 @@ export {default as quantile, quantileSorted} from "./quantile.js"; export {default as quickselect} from "./quickselect.js"; export {default as range} from "./range.js"; export {default as rank} from "./rank.js"; +export {default as linspace} from "./linspace.js"; export {default as least} from "./least.js"; export {default as leastIndex} from "./leastIndex.js"; export {default as greatest} from "./greatest.js"; diff --git a/src/linspace.js b/src/linspace.js new file mode 100644 index 00000000..ab4b59ca --- /dev/null +++ b/src/linspace.js @@ -0,0 +1,10 @@ +export default function(start, stop, n = 50, endpoint = true) { + n = Math.floor(n); + start = +start; + stop = (stop - start) / (endpoint ? n - 1 : n); + + const range = new Array(n); + for (let i = 0; i < n; ++i) range[i] = start + i * stop; + + return range; +} diff --git a/test/linspace-test.js b/test/linspace-test.js new file mode 100644 index 00000000..567628df --- /dev/null +++ b/test/linspace-test.js @@ -0,0 +1,25 @@ +import assert from "assert"; +import {linspace} from "../src/index.js"; + +it("linspace(start, stop)", () => { + assert.deepEqual(linspace(0, 49), [ + 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, + 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, + 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, + 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, + 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 + ]); +}); + +it("linspace(start, stop, n)", () => { + assert.deepEqual(linspace(2, 3, 5), [2, 2.25, 2.5, 2.75, 3]); +}); + +it("linspace(start, stop, n, false)", () => { + assert.deepEqual(linspace(2, 3, 5, false), [2, 2.2, 2.4, 2.6, 2.8]); +}); + +it("linspace(start, stop, n) descending", () => { + assert.deepEqual(linspace(5, 1, 5), [5, 4, 3, 2, 1]); + assert.deepEqual(linspace(5, 0, 5, false), [5, 4, 3, 2, 1]); +});