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Topic: Position[] bug or feature ?
Replies: 3   Last Post: Jun 25, 2013 2:53 AM

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Daniel

Posts: 56
Registered: 7/24/12
Re: Position[] bug or feature ?
Posted: Jun 25, 2013 2:53 AM
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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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