Sum of elements in 2D matrix greater tha 150

Question

Sasidharan Subramani 2020-12-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/691405-sum-of-elements-in-2d-matrix-greater-tha-150

评论： John D'Errico 2020-12-14

I wouls like to find the sum of elements in a 2D matrix (254*318) with elements value greater than 150. but I get the code run but the answer is wrong if nayone could find the erro would be very helpful.R_10M is the name of the matrix

for a = 1:254

for b = 1:318

if (R_10M(a,b) > 150)

value = sum(sum(R_10(a,b)));

end

2 个评论
显示无隐藏无

dileesh pv 2020-12-14

在 MATLAB Online 中打开

The loops in MATLAB is generally slow. MATLAB is pretty good with opearating on matrices. For a faster and efficient execution use the inherent strengths of MATLAB.

This can be done in a single step;

s = sum( R_10M (R_10M >150));

A detailed example code is given below;

R_10M = round(rand(254,318)*300); % Matrix with random entry
s = sum (R_10M (R_10M >150)); % Required sum
% Above line of code can be deconstructed into two steps as given below
a1= (R_10M >150); % Generate the logical array where the non-zero entries 
% are at the indices of elements whose values are higher than 150
s1=sum(R_10M(a1)); % sum up the elements corresponding to the non-zero 
% entries in the logical array a1

This is exactly what John D'Errico has suggested. I just added little detailed explanation to it.

John D'Errico 2020-12-14

@dileesh pv

Thank you for the explanations. I should have done that in my answer.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

VBBV 2020-12-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/691405-sum-of-elements-in-2d-matrix-greater-tha-150#answer_573110

编辑：VBBV 2020-12-12

在 MATLAB Online 中打开

for a = 1:254
    for b = 1:318
        if (R_10M(a,b) > 150)
            value(a,b) = R_10M(a,b); % use row and column indices for values matrix required before summing, 
        end
    end
end
V = sum(sum(value)); % singular value 
VV = sum(value); % vector of summed values

What you intend to sum of values > 150 in your matrix R_10, needs further specific conditions e.g. summing row wise or column wise ? or both (like you are doing inside if condition) ?