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Re: Conditional list indexing

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95908] Re: Conditional list indexing
  • From: Joerg <schaber at biologie.hu-berlin.de>
  • Date: Thu, 29 Jan 2009 05:58:44 -0500 (EST)
  • References: <glpgd4$lha$1@smc.vnet.net>

maybe not the nicest way:

Flatten[Position[# > 15 & /@ a, True]]

best,

joerg

daniele schrieb:
> Hello everybody,
> I'd like to know how I can get the indices of the elements in a list
> that satisfy a certain condition. Here's an example: suppose I have
> the list
> 
> a = Table[Prime[i],{i,10}];
> 
> that contains {2,3,5,7,11,13,17,19,23,29}.
> 
> If I execute the command
> 
> b = Select[a,#>15&];
> 
> b will contain {17,19,23,29}. I'd like to find a way to obtain a third
> list, say c, that will contain {7,8,9,10}, i.e. the indices of the
> elements in list a that are greater than 15.
> 
> Thank you,
> Daniele
> 
> 


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