How to extract values from a matrix using a row - column matrix?

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VIJENDRA
VIJENDRA 2015-4-22
评论： VIJENDRA 2015-4-23
I have a matrix like
A =
0.2180 0.5714 0.2476 0.3942 0.9253 0.5082
0.3906 0.5881 0.6529 0.3806 0.3819 0.7947
0.3381 0.0287 0.0652 0.3696 0.3735 0.1351
0.7459 0.0911 0.0163 0.7531 0.3298 0.2050
0.3690 0.5010 0.5201 0.6119 0.9038 0.1902
0.4232 0.9183 0.6523 0.2392 0.4661 0.0019
and a matrix having row and column indices
loc =
1 2
2 5
4 3
6 6
I want the extract the values of locations (1,2), (2,5), (4,3) and (6,6) from matrix A when I do this
val = A(loc(:,1),loc(:,2));
it gives me
val =
0.5714 0.9253 0.2476 0.5082
0.5881 0.3819 0.6529 0.7947
0.0911 0.3298 0.0163 0.2050
0.9183 0.4661 0.6523 0.0019
I can use diag(val); to get the locations values but is there any way so that i could get values directly without getting that square matirx
val =
0.5714
0.3819
0.0163
0.0019

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采纳的回答

Stephen23
Stephen23 2015-4-22
编辑：Stephen23 2015-4-22
Yes! You can use sub2ind to achieve this:
A = [...
0.2180 0.5714 0.2476 0.3942 0.9253 0.5082
0.3906 0.5881 0.6529 0.3806 0.3819 0.7947
0.3381 0.0287 0.0652 0.3696 0.3735 0.1351
0.7459 0.0911 0.0163 0.7531 0.3298 0.2050
0.3690 0.5010 0.5201 0.6119 0.9038 0.1902
0.4232 0.9183 0.6523 0.2392 0.4661 0.0019];
loc = [...
1 2
2 5
4 3
6 6];
X = sub2ind(size(A), loc(:,1), loc(:,2));
and then run this in the command window:
>> A(X)
ans =
0.5714
0.3819
0.0163
0.0019

更多回答（1 个）

Punit
Punit 2015-4-22
[nRows nCols ] = size(A);
A(nRows*(loc(2)-1)+loc(1))
  1 个评论
Guillaume
Guillaume 2015-4-22
This is what sub2ind does and I'd recommend using it as it works regardless of the number of dimensions of A.

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