# Subtraction between first and last element of array

**URL:** <https://discourse.nodered.org/t/subtraction-between-first-and-last-element-of-array/71965>\
**Category:** Dashboard\
**Created:** [10 December 2022 05:50 UTC](https://discourse.nodered.org/t/subtraction-between-first-and-last-element-of-array/71965 "2022-12-10T05:50:25Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Jhankhana](https://avatars.discourse-cdn.com/v4/letter/j/35a633/32.png) [@Jhankhana](https://discourse.nodered.org/u/Jhankhana)\
**Post date:** [10 December 2022 05:50 UTC](https://discourse.nodered.org/t/subtraction-between-first-and-last-element-of-array/71965/1 "2022-12-10T05:50:25Z")

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Hello!  
Sorry to bother for newb thing but I am unable to solve.  
I have return below in to function node to perform subtraction between first and last element of array. it returns length and whole array but there is something wrong with var one=Firstagg2.payload[0]; and var last= Firstagg2.payload[newMsg-1]; I have right to get first and last element. It doesn't return anyone of it and hence subtraction.

Please Help me with this!

```auto
var newMsg = { payload: msg.payload.length };
//return [newMsg, msg];

var Firstagg2 = { payload: msg.payload };
//return Firstagg2;

var one=Firstagg2.payload[0];
var last= Firstagg2.payload[newMsg-1];
msg = last-one;

return msg;

```

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<div class="post-metadata">

**Author:** ![Jhankhana](https://avatars.discourse-cdn.com/v4/letter/j/35a633/32.png) [@Jhankhana](https://discourse.nodered.org/u/Jhankhana)\
**Post date:** [10 December 2022 07:17 UTC](https://discourse.nodered.org/t/subtraction-between-first-and-last-element-of-array/71965/2 "2022-12-10T07:17:01Z")

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I am able to read var one but still not able to do for var last...

```auto
var newMsg = { payload: msg.payload.length };
//return [newMsg, msg];

var Firstagg2 = { payload: msg.payload };
//return Firstagg2;
var one = { payload: msg.payload[0]};
//return one;
var last = { payload: msg.payload[newMsg-1]};
return last;

//msg= last-one;
//return msg;

```

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**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [10 December 2022 07:23 UTC](https://discourse.nodered.org/t/subtraction-between-first-and-last-element-of-array/71965/3 "2022-12-10T07:23:37Z")

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You are over complicating it and creating unneeded objects

```auto
let array_length = msg.payload.length;
let one = msg.payload[0];
let last= msg.payload[array_length - 1];
msg.payload = last - one;
return msg;

```

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<div class="post-metadata">

**Author:** ![Jhankhana](https://avatars.discourse-cdn.com/v4/letter/j/35a633/32.png) [@Jhankhana](https://discourse.nodered.org/u/Jhankhana)\
**Post date:** [10 December 2022 09:11 UTC](https://discourse.nodered.org/t/subtraction-between-first-and-last-element-of-array/71965/4 "2022-12-10T09:11:32Z")

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Thank you !

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [24 December 2022 09:12 UTC](https://discourse.nodered.org/t/subtraction-between-first-and-last-element-of-array/71965/5 "2022-12-24T09:12:13Z")

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