Re: Manipulating vectors with Position

• To: mathgroup at smc.vnet.net
• Subject: [mg117380] Re: Manipulating vectors with Position
• From: Heike Gramberg <heike.gramberg at gmail.com>
• Date: Wed, 16 Mar 2011 06:30:34 -0500 (EST)

```Shouldn't the output in your example be {{a}, {b+d+e}, {c+f}}?
If that's the case, then one way to do what you want is

Map[{Total[Array1[[#]]]} &, Array2, {1}]

Heike.

On 15 Mar 2011, at 11:07, Lengyel Tamas wrote:

> Dear Mathworld Users,
> I am tackling a rather straightforward problem. Here it is.
>
> 1) I have generated an array of values (Array1)
> 2) I have generated an array of vectors in Array2, whose Length varies,
> and in each subvector the numbers contain the Position (index) of those
> elements that I need from Array1. So far so good.
>
> 3) What I need is to create a code that picks out those elements from
> Array 1 and ads them together if Array2's subvectors have more than 1
> element.
>
> Here's an example to make it clear:
>
> Array1 = {a,b,c,d,e,f};  (*a;;f are numbers*)
> Array2 = {{1}, {2,4,5}, {3,6}};
>
> My outpout should be: {{a}, {a+d+e}, {c+f}}
>
> I think it is simple, but I can't seem to do it.
>
> Any ideas?
>
> Thank you.
>
> Tam=E1s
>

```

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