Question

我想在3d矩阵中返回单元格周围的8个单元格的索引和值。

mat = rand(5,5,5);

% Cell of interest
pos = [3 3 3]
pos_val = mat(pos(1), pos(2), pos(3))

% Surrounding cells
surrounding_pos = [pos(1)-1:pos(1)+1; pos(2)-1:pos(2)+1; pos(2)-1:pos(2)+1]
surrounding_val = mat(surrounding_pos(1,:), surrounding_pos(2,:), surrounding_pos(3,:))

这适用于矩阵中心的值，但如果pos位于边缘，则会中断。（例如，如果pos为[3,4,5]，则surround_pos将包含[3,4,6]，其超出范围）

我显然可以删除around_pos值＆lt; 0或＆gt; size（mat），但这似乎不是一个非常简单的MATLAB方法。有任何想法吗？

Answer 1

与讨论here相同的解决方案，但扩展到多个（任何）维度：

mat = randi(10,5,5,5);
siz = size(mat );
N = numel(siz); % number of dimensions
M = 1; % surrounding region size

pos = [3 3 3];
pos_val = mat(pos(1), pos(2), pos(3));

surrounding_pos = cell(N,1);
for ii=1:N
    surrounding_pos{ii} = max(1,pos(ii)-M):min(siz(ii),pos(ii)+M);
end
surrounding_val2 = mat(surrounding_pos{:});

重要的部分是最后四行，它避免了为每个维度c / p最大，最小的东西..

或者，如果您喜欢短代码，则循环更改为arrayfun：

surrounding_pos = arrayfun(@(ii) max(1,pos(ii)-M):min(siz(ii),pos(ii)+M), 1:N,'uni',false);
surrounding_val2 = mat(surrounding_pos{:});

Answer 2

这是一个整理版本。欢呼声。

mat = rand(5,5,5);
N = size(mat)
if length(N) < 3 || length(N) > 3; error('Input must be 3 dimensional'); end;
pos = [1 3 5]
surrounding_val = mat(max(pos(1)-1, 1):min(pos(1)+1, N(1)), max(pos(2)-1, 1):min(pos(2)+1, N(2)), max(pos(3)-1, 1):min(pos(3)+1, N(3)))

编辑：添加了错误陷阱。

Answer 3

我发现这篇文章是因为我需要抓住Matrix中所选点的周围索引。看起来这里的答案正在返回周围值的矩阵，但问题也是对周围指数感兴趣。我能够用“try / catch”语句做到这一点，我之前在MATLAB中不知道这些语句。对于2D矩阵，Z：

%Select a node in the matrix
Current = Start_Node;

%Grab its x, y, values (these feel reversed for me...)
C_x = rem(Start_Node, length(Z));
if C_x ==0
    C_x =length(Z);
end
C_y = ceil(Start_Node/length(Z));
C_C = [C_x, C_y];

%Grab the node's surrounding nodes.
try
    TRY = Z(C_x - 1, C_y);
    Top = Current -1;
catch
    Top = Inf;
end
try
    TRY = Z(C_x + 1, C_y);
    Bottom = Current +1;
catch
    Bottom = Inf;
end
try
    TRY = Z(C_x, C_y + 1);
    Right = Current + length(Z);
catch
    Right = Inf;
end
try
    TRY = Z(C_x, C_y - 1);
    Left = Current - length(Z);
catch
    Left = Inf;
end

surround = [Top, Bottom, Left, Right];
m = numel(surround == inf);
k = 1;
%Eliminate infinites.

surround(surround==inf) =[];

我希望有人发现这些信息相关。

三维矩阵中周围单元的索引和值

3 个答案: