问题描述
我有这个 i x j x k 3d 矩阵(这是一部电影).在没有循环的情况下，我试图取每个 ixj 数组中非零正元素的平均值，并将这些值放入一个 1x1xk 矩阵中.
I have this i x j x k 3d matrix (it's a movie). Without loops, I'm trying to take the mean of the non-zero positive elements in each ixj array and put these values into a 1x1xk matrix.
我已经搜索了很长时间了，虽然有很多解决方案可以为 2d 矩阵实现这一点，但我一生都无法找到一种方法来为 3d 矩阵做到这一点而不使用循环.
I've been searching for quite a while now, and although there's plenty of solutions to accomplish this for a 2d matrix, I can't for the life of me find a way to do it for a 3d matrix without using a loop.
推荐答案
如果将每个图像(帧)转换为数组会怎样:
What if you convert each image (frame) into an array:
% Remove negative and zero elements
A(A<=0) = 0;
% Convert each image into array
B = reshape(A,[Nimg,Nfrm]);
% Extract mean value of each image
C = mean(B,1);
其中 Nimg 是每个图像中的像素数，Nfrm 是图像数.
where Nimg is the number of pixels in each image and Nfrm is the number of images.
如果您不想在均值分母中包含非零和负数(如@Dan 建议的那样)，只需使用以下行缩放结果:
If you don't want to include the non-zero and negative numbers in the mean denominator (as @Dan suggests), just scale the result with the following line:
C_Dan = C.*squeeze(Nimg./sum(sum(A>0))).';
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