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Re: Problem with Position

  • To: mathgroup at smc.vnet.net
  • Subject: [mg119648] Re: Problem with Position
  • From: Dominic Wörner <dominic.woerner at mpi-hd.mpg.de>
  • Date: Thu, 16 Jun 2011 03:59:59 -0400 (EDT)
  • References: <201106151120.HAA22862@smc.vnet.net> <BANLkTindQ9jZN_wLzsAy9pTM+Udt3T+K2g@mail.gmail.com>

Hi Leonid,

Many thanks for your advise but I still have one problem

When I write to a file using WriteString[str, ToString[number]] it will 
be written in OutputForm. Now I thought using your advice It should work 
with Position[..., x_/;x==OutputForm[number]]
but unfortunately it doesn't
Am 15.06.2011 um 12:59 schrieb Leonid Shifrin:

> Hi Dominic,
>
> This is most likely a symbolic/numerical issue. Position is based on 
symbolic rather than numeric comparisons.
> You may have success with
>
> Flatten@Position[data[[All,1]],x_/;x==0.785398]
>
> Here is one of the most recent related discussions:
>
> http://stackoverflow.com/questions/5750623/using-position-correctly
>
> Regards,
> Leonid
>
>
> On Wed, Jun 15, 2011 at 3:20 PM, Dominic W=F6rner 
<dominic.woerner at mpi-hd.mpg.de> wrote:
> Hi,
>
> I have to import data from a csv file. And I get a structure 
data[[rows]]={first, second,...}.
> Now I want to find the rows in which, say the first entry has a 
specific values.
> By just looking at the data there are for example entries with value 
0.785398.
> But when I try Flatten@Position[data[[All,1]],0.785398] or with 
ToString[0.785398] I just get {}
>
> What's the problem here?
>
> Best,
> Dominic
>
>


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