From bc3cbbcb20ae9bcf40e409e4f94b901a398d633d Mon Sep 17 00:00:00 2001
From: Tom Hickson <thomasjhickson@gmail.com>
Date: Wed, 8 Apr 2020 18:55:37 +0100
Subject: [PATCH] Diff function

---
 src/function/matrix/diff.js | 46 +++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 src/function/matrix/diff.js

diff --git a/src/function/matrix/diff.js b/src/function/matrix/diff.js
new file mode 100644
index 000000000..1d357fe02
--- /dev/null
+++ b/src/function/matrix/diff.js
@@ -0,0 +1,46 @@
+import { factory } from '../../utils/factory'
+import { isMatrix } from '../../utils/is'
+
+const name = 'diff'
+const dependencies = ['typed', 'matrix']
+
+export const createDiff = /* #__PURE__ */ factory(name, dependencies, ({ typed, matrix }) => {
+  /**
+   * Create a new matrix or array of the difference between elements of the given array
+   *
+   * Syntax:
+   *
+   *     math.diff(x)
+   *
+   * Examples:
+   *
+   *     const arr = [1, 2, 4, 7, 0]
+   *     math.diff(arr) // returns [1, 2, 3, -7]
+   *
+   * @param {Array | Matrix } x     An array or matrix
+   * @return {Array | Matrix}       Difference between array elements
+   */
+  return typed(name, {
+    'Array | Matrix, function': function (x) {
+      if (isMatrix(x)) {
+        return matrix(_ArrayDiff(x.toArray(), diff))
+      } else {
+        return _ArrayDiff(x)
+      }
+    }
+  })
+
+  /**
+   * 
+   * @param {Array} arr         An array
+   * @return {Array}            resulting array
+   */
+  function _ArrayDiff (arr) {
+    const result = []
+    const size = arr.length
+    for (let i = 1; i < size; i++) {
+      result.push(arr[i] - arr[i-1])
+    }
+    return result
+  }
+})
\ No newline at end of file