---
id: 5d7925398157757b23730fdd
title: Part 121
challengeType: 0
dashedName: part-121
---
# --description--
The `reduce` method can take a second argument (in addition to the function), specifying the initial accumulator value. In this case, the current value starts from index 0 rather than index 1:
```js
[1, [1, 2, 3], [3, 4, 5]].reduce((a, x) => a.concat(x), []); // [1, 1, 2, 3, 3, 4, 5]
// without the second argument, it first tries 1.concat([1, 2, 3]), but 1 is not an array
// now it first tries [].concat(1) which works
```
Add a function `nodups` to `spreadsheetFunctions`, with the value `arr => arr.reduce((a, x) => a.includes(x), [])`.
# --hints--
See description above for instructions.
```js
assert(
/nodups['"]?:arr=>arr\.reduce\(\(a,x\)=>a\.includes\(x\),\[\]\)/.test(
code.replace(/\s/g, '')
)
);
```
# --seed--
## --before-user-code--
```html
Spreadsheet
```
## --after-user-code--
```html
```
## --seed-contents--
```html
```
# --solutions--
```html
```