Conditional list indexing

*To*: mathgroup at smc.vnet.net*Subject*: [mg95855] Conditional list indexing*From*: daniele <danielelinaro at gmail.com>*Date*: Wed, 28 Jan 2009 06:43:39 -0500 (EST)

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