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Re: Conditional list indexing

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95915] Re: Conditional list indexing
  • From: dh <dh at metrohm.com>
  • Date: Thu, 29 Jan 2009 06:00:01 -0500 (EST)
  • References: <glpgd4$lha$1@smc.vnet.net>


Hi Daniele,

you could e.g. use:

a = Table[Prime[i], {i, 10}];

b = Select[a, # > 15 &];

Position[a, #] & /@ b // Flatten

hope this helps, Daniel





daniele wrote:

> 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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