Re: Problem with Position applied on 2D list?

• To: mathgroup at smc.vnet.net
• Subject: [mg72622] Re: Problem with Position applied on 2D list?
• From: dh <dh at metrohm.ch>
• Date: Fri, 12 Jan 2007 06:13:51 -0500 (EST)
• References: <eo4n23\$l4i\$1@smc.vnet.net>

```
Hi Heiko,

the problem with your code is that "_" matches everything ( e.g. the

head). This works if the match part must contain 5 e.g.the head does not

contain 5). But it fails badly otherwise. Therefore, you must be more

specific, e.g. instead of "_" the more specific: "{_Integer ..}".

Daniel

Heiko Damerau wrote:

> Dear All,

>

>      There is some strange behaviour of the Position[] function I am

> struggling with:

>

> integerRandomTable = Table[Table[Random[Integer, 10], {10}], {10}];

>

> Find the position of all lists containing the value 5 (just a simple

> example):

>

> Position[integerRandomTable, _?(MemberQ[#, 5] &)]

>

> gives the expected result, e.g. {{1}, {3}, {4}, {5}, {6}, {7}, {8}}.

> However, just asking for all lists not containing the value 5

>

> Position[integerRandomTable, _?(Not[MemberQ[#, 5]] &)]

>

> Doesn't give the expected result but some strange thing, e.g. {{0},

> {1,0}, {1, 1}, {1, 2}, {1, 3}, {1, 4}, ..., {10, 3}, {10, 4}, {10, 5},

> {10, 6}, {10, 7}, {10, 8}, {10, 9}, {10, 10}, {10}, {}}

>

>      What is the explanation for the different behaviour of MemberQ[]

> and Not[MemberQ[]]?

>

>      Thanks a lot in advance for any help.

>

> Best regards,

> Heiko

>

```

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