Re: reading different locations of a matrix specified by indices

*To*: mathgroup at smc.vnet.net*Subject*: [mg113895] Re: reading different locations of a matrix specified by indices*From*: Albert Retey <awnl at gmx-topmail.de>*Date*: Wed, 17 Nov 2010 05:30:20 -0500 (EST)*References*: <ibtl2m$5mf$1@smc.vnet.net>

Am 16.11.2010 11:06, schrieb Nasser M. Abbasi: > Given a matrix A, and list of locations withing the matrix, > where each location is given by {i,j} entry, I wanted to > find the most efficient and clear way to obtain the entries > in the matrix by these locations. > > I wanted to ask the experts here what they think of this > method, and if they can suggest a better way. > > Example, given > > A={{1,2,3}, > {4,5,6}, > {7,8,9}} > > and wanted to obtain the entries at say {1,1} and {3,3}, > which will be 1 and 9 in this example. So I first made a > list of the locations : > > pos={ {1,1},{3,3}}; > > Then typed > > Map[ A[[Sequence@@ # ]] & , pos ] > > and got back > > {1,9} > So, this seems to work. > > Any suggestion of may be of a more 'obvious' or better way? how about this: Extract[A, pos] hth, albert