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Position

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  Position "Joerg Schroeder" <sd-gymwalsrode@gmx.de> - 2011-05-25 09:55 +0000
    Re: Position David Bailey <dave@removedbailey.co.uk> - 2011-05-25 23:32 +0000
    Re: Position Roland Franzius <roland.franzius@uos.de> - 2011-05-25 23:30 +0000
    Re: Position Wolfgang Windsteiger <Wolfgang.Windsteiger@risc.jku.at> - 2011-05-25 23:31 +0000

#2687 — Position

Dear Group,

I don't understand the following:

I have a list of data and want to find the position of special elements:

data=Table[CDF[BinomialDistribution[150,0.3],k],{k,0,150}]

Position[data,#>=0.95&]

With this I get {} (null set) as an answer, whereas for example Select gives the answer I expect.

Select[data,#>=0.95&]

Do I do something wrong with Position?

Thanks

Jorg Schroder
-- 
Dr. Jörg Schröder
Gymnasium Walsrode
Sunderstrasse 19
29664 Walsrode

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#2711

On 25/05/2011 10:55, Joerg Schroeder wrote:
> Dear Group,
>
> I don't understand the following:
>
> I have a list of data and want to find the position of special elements:
>
> data=Table[CDF[BinomialDistribution[150,0.3],k],{k,0,150}]
>
> Position[data,#>=0.95&]
>
> With this I get {} (null set) as an answer, whereas for example Select gives the answer I expect.
>
> Select[data,#>=0.95&]
>
> Do I do something wrong with Position?
>
> Thanks
>
> Jorg Schroder
Position is looking for a pattern - it doesn't take a function argument 
like Select.

In[11]:= Position[{0.1, 1.0, 0.8, 1.1, 3.3}, x_ /; x > 0.95]

Out[11]= {{2}, {4}, {5}}

David Bailey
http://www.dbaileyconsultancy.co.uk

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#2723

Am 25.05.2011 11:55, schrieb Joerg Schroeder:
> Dear Group,
>
> I don't understand the following:
>
> I have a list of data and want to find the position of special elements:
>
> data=Table[CDF[BinomialDistribution[150,0.3],k],{k,0,150}]
>
> Position[data,#>=0.95&]
>
> With this I get {} (null set) as an answer, whereas for example Select gives the answer I expect.
>
> Select[data,#>=0.95&]
>
> Do I do something wrong with Position?

Position searches  patterns

Position[data, _?(# >= 0.95 &)]

-- 

Roland Franzius

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#2725

Position needs a *pattern*, not a condition. Like what you would write 
in Cases[data,...] when used instead of Select[data,...] in order to 
filter elements.

WW.

On 05/25/2011 11:55 AM, Joerg Schroeder wrote:
> Dear Group,
>
> I don't understand the following:
>
> I have a list of data and want to find the position of special elements:
>
> data=Table[CDF[BinomialDistribution[150,0.3],k],{k,0,150}]
>
> Position[data,#>=0.95&]
>
> With this I get {} (null set) as an answer, whereas for example Select gives the answer I expect.
>
> Select[data,#>=0.95&]
>
> Do I do something wrong with Position?
>
> Thanks
>
> Jorg Schroder

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