Groups > comp.soft-sys.math.mathematica > #15001

Re: Position[] bug or feature ?

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From	Daniel <dosadchy@its.jnj.com>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Re: Position[] bug or feature ?
Date	Tue, 25 Jun 2013 06:53:33 +0000 (UTC)
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> Dear Group
> 
> When trying to evaluate the following code the
> expected result is returned.
> But strangly there is an error message generated.
> The code should (and does) return the positions of
> all sublists with an even element at the second
> position.
> 
> 
> 
> Position[{{1, 2}, {2, 3}, {1, 4}}, _?(EvenQ[#[[2]]]
> &), {1}]
> 
> Part::partd: Part specification List[[2]] is longer
> than depth of object. >>
> 
> {{1}, {3}}
> 
> 
> 
> Any hints if this a bug or a feature ?
> 
> Regards Robert
> 

Expression head is also on level 1, and the Position[] function includes heads in the search by default. And obviously, when trying to check the head "List", it cannot calculate EvenQ[List[[2]]]

This works:

Position[{{1, 2}, {2, 3}, {1, 4}}, _?(EvenQ[#[[2]]] &), {1}, Heads -> False]

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Re: Position[] bug or feature ? Daniel <dosadchy@its.jnj.com> - 2013-06-25 06:53 +0000

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