       Re: Select from Tuplet using logical expression

• To: mathgroup at smc.vnet.net
• Subject: [mg116856] Re: Select from Tuplet using logical expression
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Wed, 2 Mar 2011 04:36:30 -0500 (EST)

```On 3/1/11 at 5:20 AM, lt648 at hszk.bme.hu (Lengyel Tamas) wrote:

>Skip if needed:
>///I am working on a part combinatorical problem with sets of 3
>differently indexed values (e.g. F_i, F_j, F_k, F denoting frequency
>channels) which are subsets of many values (e.g 16 different
>frequency channels, denoted F_0, F_1 ... F_15).

>Now, I need to select triplets from these channels, I used Tuplets.
>So far so good. From these I need those combinations where indexes
>i!=k and/or j!=k, and i=j is allowed (e.g {i,j,k} = {12, 12, 4} is=
a
>valid channel combination, but {3, 12, 3} is not).///

>So basically I need to generate triplets from a range of integer
>numbers, where the first and second elements of these triplets do
>not match the third. I thought Select would help, but I don't know
>if there exists an option to control elements' values in a
>condition.

>From then on I must use these triplets' elements in a function.

>But first I am asking your help in generating thos triplets of
>numbers.

Perhaps something like

DeleteCases[Tuples[Range, 3], {a_, a_, a_} | {a_, _, a_}]

will do well enough for you. But note, doing Tuples[Range]
generates all possible triplets with the integers from 1 to 3,
including those you don't want. So, if your range of integers is
large, this method may not be satisfactory as it will consume
quite a bit of memory. It is a brute force rather than efficient method.

```

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