       Re: Handling conditions on subvector elements

• To: mathgroup at smc.vnet.net
• Subject: [mg117582] Re: Handling conditions on subvector elements
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Wed, 23 Mar 2011 02:55:42 -0500 (EST)

```On 3/22/11 at 5:05 AM, lt648 at hszk.bme.hu (Lengyel Tamas) wrote:

>I am struggling with a piece of code which should result in a List :

>1) I have a vector with subvectors with triplets of values. 2) What
>I wish to achieve is a cycle that returns with a List with either
>'1's or '2's in it. 3) The cycle should check whether the first and
>second element in subvectors are equal and neither of them are equal
>with the third, if so, return 1;
>If all the elements are unequal, return 2

>E.g.

>V= {{1,1,2},{1,1,3},{2,3,1},{1,2,3},{3,3,1}} should return with {1,
>1, 2, 2,1}

>I'm assuming 'If' should be the key (as it returns 2 types of
>values), but I can't seem to do it properly.

Here are a few ways to achieve what you want. First using If

In:= If[Length[Union[#]] == 3, 2, 1] & /@ v

Out= {1,1,2,2,1}

Next using pattern matching

In:= v /. {{___, a_, ___, a_, ___} -> 1, {a_, b_, c_} -> 2}

Out= {1,1,2,2,1}

Note the order of the replacement rules is important.

And finally a direct computation

In:= Length[Union[#]] - 1 & /@ v

Out= {1,1,2,2,1}

Note this last is probably the fastest solution of the three
here but is less general. The first two solutions will return 1
if all three elements are identical while this last will return
0 in that case.

```

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