Re: Re: Not[OddQ] is not the same as EvenQ (sometimes)
- To: mathgroup at smc.vnet.net
- Subject: [mg3957] Re: [mg3899] Re: Not[OddQ] is not the same as EvenQ (sometimes)
- From: Allan Hayes <hay at haystack.demon.co.uk>
- Date: Sat, 11 May 1996 23:53:20 -0400
- Sender: owner-wri-mathgroup at wolfram.com
Dave Wagner<wagner at motel6.cs.colorado.edu>
in [mg3899] Re: Not[OddQ] is not the same as EvenQ (sometimes)
writes
>>Position[{2,3,4,5,6,7}, x_?(!NumberQ[#]&)]
>>{{0}, {}}
>I don't know the cause of the empty set of list braces here.
Dave:
The empty index sequence is the index of the whole expression:
Position[{1,{3}},{1,{3}}]
{{}}
{1,{3}}[[]]
{1, {3}}
The index gives directions starting from the whole expression --
with no directions we go nowhere.
Allan Hayes
hay at haystack.demon.co.uk
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