Merge branch 'count' of https://github.com/Fil/d3-array into Fil-count

Author: mbostock

README.md

@@ -341,6 +341,16 @@ Map(3) {
 
 To convert a Map to an Array, use [Array.from](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from). See [d3.group](#group) for examples.
 
+<a name="count" href="#count">#</a> d3.<b>count</b>(<i>iterable</i>[, <i>accessor</i>]) · [Source](https://github.com/d3/d3-array/blob/master/src/count.js "Source")
+
+Returns the number of valid number values (*i.e.*, not null, NaN, or undefined) in the specified *iterable*; accepts an accessor.
+
+For example:
+
+```js
+d3.count([{n: "Alice", age: NaN}, {n: "Bob", age: 18}, {n: "Other"}], d => d.age) // 1
+```
+
 <a name="cross" href="#cross">#</a> d3.<b>cross</b>(<i>...iterables</i>[, <i>reducer</i>]) · [Source](https://github.com/d3/d3-array/blob/master/src/cross.js), [Examples](https://observablehq.com/@d3/d3-cross)
 
 Returns the [Cartesian product](https://en.wikipedia.org/wiki/Cartesian_product) of the specified *iterables*. For example, if two iterables *a* and *b* are specified, for each element *i* in the iterable *a* and each element *j* in the iterable *b*, in order, invokes the specified *reducer* function passing the element *i* and element *j*. If a *reducer* is not specified, it defaults to a function which creates a two-element array for each pair:

src/count.js

@@ -0,0 +1,18 @@
+export default function count(values, valueof) {
+ let count = 0;
+ if (valueof === undefined) {
+ for (const value of values) {
+ if (value != null && value >= value) {
+ ++count;
+ }
+ }
+ } else {
+ let index = -1;
+ for (let value of values) {
+ if ((value = valueof(value, ++index, values)) != null && value >= value) {
+ ++count;
+ }
+ }
+ }
+ return count;
+}

src/index.js

@@ -1,6 +1,7 @@
 export {default as bisect, bisectRight, bisectLeft} from "./bisect.js";
 export {default as ascending} from "./ascending.js";
 export {default as bisector} from "./bisector.js";
+export {default as count} from "./count.js";
 export {default as cross} from "./cross.js";
 export {default as descending} from "./descending.js";
 export {default as deviation} from "./deviation.js";

test/count-test.js

@@ -0,0 +1,24 @@
+var tape = require("tape"),
+ arrays = require("../");
+
+tape("count() accepts an iterable", function(test) {
+ test.deepEqual(arrays.count([1, 2]), 2);
+ test.deepEqual(arrays.count(new Set([1, 2])), 2);
+ test.deepEqual(arrays.count(generate(1, 2)), 2);
+ test.end();
+});
+
+tape("count() ignores NaN, null", function(test) {
+ test.deepEqual(arrays.count([NaN, null, 0, 1]), 2);
+ test.end();
+});
+
+tape("count() accepts an accessor", function(test) {
+ test.deepEqual(arrays.count([{v:NaN}, {}, {v:0}, {v:1}], d => d.v), 2);
+ test.deepEqual(arrays.count([{n: "Alice", age: NaN}, {n: "Bob", age: 18}, {n: "Other"}], d => d.age), 1);
+ test.end();
+});
+
+function* generate(...values) {
+ yield* values;
+}