Re: DeleteCases

• To: mathgroup at smc.vnet.net
• Subject: [mg98182] Re: DeleteCases
• From: Szabolcs Horvát <szhorvat at gmail.com>
• Date: Wed, 1 Apr 2009 05:58:51 -0500 (EST)
• References: <gqsn69\$3qp\$1@smc.vnet.net>

```Filippo Miatto wrote:
> Dear all,
> Given this example list:
>
> {{0, 0, 1, 1}, {0, 0, 2, 2}, {0, 0, 3, 3}, {1, 1, 0, 0}, {1, 1, 2, 2},
> {1, 1, 3, 3}, {2, 2, 0, 0}, {2, 2, 1, 1}, {2, 2, 3, 3}, {3, 3, 0, 0},
> {3, 3, 1, 1}, {3, 3, 2, 2}}
>
> I need the elements {a,a,b,b} and {b,b,a,a} to be the same, i.e. i
> want to delete one of the two occurrences from the list. (or all but
> one if the condition is more complicated, say {a,b,c,d} and {b,a,c,d}
> or {a,b,c,d} and {a,b,d,c})
> How can i do that? Can i use DeleteCases? if so, what conditional
> should I use to compare different elements in the list?
> I tried without success for all the night.. (it's 6.15AM now!)
> Thank you,
>

Use Union[] with a custom SameTest,

Union[{{0, 0, 1, 1}, {0, 0, 2, 2}, {0, 0, 3, 3}, {1, 1, 0, 0}, {1, 1,
2, 2}, {1, 1, 3, 3}, {2, 2, 0, 0}, {2, 2, 1, 1}, {2, 2, 3, 3}, {3,
3, 0, 0}, {3, 3, 1, 1}, {3, 3, 2, 2}},
SameTest -> (#1[[{3, 4, 1, 2}]] === #2 &)]

```

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