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snippets/js/s/accumulate.md

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+---
+title: Partial sum array
+type: snippet
+language: javascript
+tags: [math]
+author: chalarangelo
+cover: river-house-lights
+dateModified: 2022-01-30T13:10:13+02:00
+---
+
+Creates an array of partial sums.
+
+- Use `Array.prototype.reduce()`, initialized with an empty array accumulator to iterate over `nums`.
+- Use `Array.prototype.slice()` to get the previous partial sum or `0` and add the current element to it.
+- Use the spread operator (`...`) to add the new partial sum to the accumulator array containing the previous sums.
+
+```js
+const accumulate = (...nums) =>
+  nums.reduce((acc, n) => [...acc, n + (acc.slice(-1)[0] || 0)], []);
+```
+
+```js
+accumulate(1, 2, 3, 4); // [1, 3, 6, 10]
+accumulate(...[1, 2, 3, 4]); // [1, 3, 6, 10]
+```