       Re: Manipulating vectors with Position

• To: mathgroup at smc.vnet.net
• Subject: [mg117376] Re: Manipulating vectors with Position
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Wed, 16 Mar 2011 06:29:50 -0500 (EST)

```On 3/15/11 at 6:07 AM, lt648 at hszk.bme.hu (Lengyel Tamas) wrote:

>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}}

Did you perhaps make a typo here? Based on your description I
would have expected the output to be {{a}, {b+d+e}, {c+f}} since
the second set of indices starts with 2 rather than 1. Assuming
you did make a typo and you do want the output to be as I would
expect from your description this can be done as:

In:= {Plus @@ array1[[#]]} & /@ array2

Out= {{a}, {b + d + e}, {c + f}}

or

In:= {Total@array1[[#]]} & /@ array2

Out= {{a}, {b + d + e}, {c + f}}

```

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