Cross validation: Loop with unbalanced length

2 次查看（过去 30 天）
Kamu
Kamu 2017-4-29
编辑： Kamu 2017-4-29
Hi all,
it might be a simple question but I would like to ask for a neat way how to write a loop for the following problem:
Let's say I have an array A=A(1), A(2).. A(n) and B=B(1), B(2).. B(m). I first want to do some calculations in a way that:
  1. First iteration: A(1) with B(1), B(2).. B(m)
  2. Second iteration: A(2) with B(1), B(2).. B(m)
  3. till: A(n) with B(1), B(2).. B(m)
Explanation of the problem: I have 2 binary images, let us name them A and B. The centroid coordinates were obtained from A and I want to know if it is inside a given area in image B. The number of centroid and area are unbalanced (e.g. 10 centroids, and 6 area). Each centroid can be assigned to a specific polygon and delete those centroids that could not determine within any polygon.
My starting code:
numA = 10;
numB = 5;
for u=1:numA
coordinate = imageA(u).Centroid;
xCentroid = coordinate(:, 2);
yCentroid = coordinate(:, 1);
for v=1:numB
area = imageB(v).PixelList;
xArea = area(:, 2);
yArea = area(:, 1);
% Check if centroid is within area
[in, out] = inpolygon(xCentroid, yCentroid, xArea, yArea);
end
end
  1 个评论
Stephen23
Stephen23 2017-4-29
编辑：Stephen23 2017-4-29
The simplest solution would be to put all of the "some operations" into a function, and then call it using bsxfun. It would require just one simple line of code:
bsxfun(fun,A(:),B(:).')
After all, repeated code should be put into functions anyway:
https://www.mathworks.com/matlabcentral/answers/228557-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users

请先登录，再进行评论。

请先登录，再回答此问题。

回答（2 个）

Geoff Hayes
Geoff Hayes 2017-4-29
Kamu - you could try something like
N = 42;
M = 84;
A = randi(255,N,1);
B = randi(255,M,1);
for u=1:N
a = A(u);
for v=1:M
b = B(v);
% do some calculation with a and b
end
end
In the above, the outer loop iterates over each element of A and the inner loop over each element of B which should satisfy your requirements of fixing an element of A and using it with all elements of B.1
  1 个评论
Kamu
Kamu 2017-4-29
编辑：Kamu 2017-4-29
Dear Geoff, thanks for your suggestion. However, it seems to be more complicated. Please find below my code:
numA = 10;
numB = 5;
for u=1:numA
coordinate = imageA(u).Centroid;
xCentroid = coordinate(:, 2);
yCentroid = coordinate(:, 1);
for v=1:numB
area = imageB(v).PixelList;
xArea = area(:, 2);
yArea = area(:, 1);
% Check if centroid is within area
[in, out] = inpolygon(xCentroid, yCentroid, xArea, yArea);
end
end
table = repmat(struct('IndexofA',[], 'Location', []), numA, 1);
So the idea is that I want to know if the Centroid is within a given polygon. The total number of centroid and polygon is unequal. The result should be stored in a structure element. The overall goal is to assign each centroid to a specific polygon and delete those centroids that could not determine within any polygon.
I hope this will make it clear and thanks again for your time and help.

请先登录，再进行评论。

Image Analyst
Image Analyst 2017-4-29
I'll bet anything you got imageA(u) from doing this:
imageA = regionprops(labeledImage, 'Centroid');
Am I right? And you want to find out if the centroid is in the shape, like it's an O shape, or outside the shape, like a "C" shape. If you're willing to round the centroid to the nearest pixel, then you can use ismember or intersect(). Untested code:
imageA = regionprops(labeledImage, 'Centroid', 'PixelList);
for k = 1 : length(imageA)
if ~isempty(intersect(imageA(k).Centroid, imageA(k).PixelList, 'rows'))
% Centroid is one of the blob pixels.
else
% Centroid is not one of the blob pixels.
end
end
  1 个评论
Kamu
Kamu 2017-4-29
编辑：Kamu 2017-4-29
Dear Image Analyst,
thanks for your answer. Your bet was close to what I would like to do. Please allow me to explain it again: I have 2 binary images, let us name them A and B. The centroid coordinates were obtained from A and I want to know if it is inside a given area in image B. The number of centroid and area are unbalanced (e.g. 10 centroids, and 6 area).

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Images 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by