2.20 extract values from matrix given their index

Given a matrix A, and list of locations within the matrix, where each location is given by \(i,j\) entry, find the value in the matrix at these locations

Example, given

A={{1,2,3}, 
   {4,5,6}, 
   {7,8,9}}
 

obtain the entries at \(1,1\) and \(3,3\) which will be \(1\) and \(9\) in this example.

Mathematica mat={{1,2,3}, {4,5,6}, {7,8,9}} pos = { {1,1},{3,3}}; Map[ mat[[Sequence@@ # ]] & , pos ]	{1,9}
Another method (same really as above, but using Part explicit) Map[Part[A, Sequence @@ #] &, pos]	{1,9}

 

Matlab A=[1 2 3; 4 5 6; 7 8 9]; I=[1 3]; % setup the I,J indices J=[1 3]; A(sub2ind(size(A),I,J))

ans = 1 9

 

Maple A:=Matrix([[1,2,3],[4,5,6],[7,8,9]]); loc:=[[1,1],[3,3]]; map(x->A[op(x)],loc);

[1, 9]