Re: List operations

• To: mathgroup at smc.vnet.net
• Subject: [mg25447] Re: List operations
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Sun, 1 Oct 2000 02:44:29 -0400 (EDT)
• References: <8r196t\$hs8@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Mat,
Two ideas:

Cases[data, {x_, y_} /; 3x + y^2 == 7]

{{1, 2}, {2, 1}}

op[{x_, y_}] := 3x + y^2
Select[data, op[#] == 7 &]

{{1, 2}, {2, 1}}

--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Matt Herman" <Henayni at hotmail.com> wrote in message
news:8r196t\$hs8 at smc.vnet.net...
>
> Hi,
>
> Suppose I have a list of ordered pairs {{a1,b1},{a2,b2},...,{an,bn}}.
> What is an efficient way of pulling out all the pairs such that, if I do
> an operation on the first element in the list, and another on the
> second, and I sum them, they equal some predetermined constant?
>
> For instance, say 3*listpart[[1]]+listpart[[2]]^2
>
> Thanks
>
>

```

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