Array average and range initialization

snippets/average-of-array-of-numbers.md

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+### Average of array of numbers
+
+Use `reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
+
+```js
+var average = arr =>
+  arr.reduce( (acc , val) => acc + val, 0) / arr.length;
+```

snippets/initialize-array-with-range.md

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+### Initialize array with range
+
+Use `Array(end-start)` to create an array of the desired length, `map()` to fill with the desired values in a range.
+You can omit `start` to use a default value of `0`.
+
+```js
+var initializeArrayRange = (end, start = 0) =>
+  Array.apply(null, Array(end-start)).map( (v,i) => i + start );
+```