How to find mean of a vector including only a specific range of elements

Question

Sandie Nhatien Vu 2016-8-5

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https://ww2.mathworks.cn/matlabcentral/answers/298633-how-to-find-mean-of-a-vector-including-only-a-specific-range-of-elements

编辑： Sandie Nhatien Vu 2016-8-6

I am new with matlab, in advance sorry for my question. How can I find the mean of a vector that only takes elements between 15 and 25.

Ex.

I have a vector: v = [20 8 15 19 7 31]

What i want as output for this vector is (20+15+19)/3 = 18.

I know that the equation to use is:

sum(v)/length(v) = mean(v)

but i only want to include elements from 15:25 in any(!) vector.

My question: How can l write a program that computes and returns the mean, taking only the valid measurement (15-25)? This is regarding both vectorization and/loops

So far i have this code:

 function averageRate = fermentationRate(vector)
averageRate = 0;
for k = 1:length(vector)
    if (vector(k) < 25 && vector(k) > 15)
        averageRate = (averageRate + vector(k));
    end
end

That only tells the sum of the vector, i miss the dividing by length(vector). How can l add this?

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Answer 1

James Tursa 2016-8-6

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https://ww2.mathworks.cn/matlabcentral/answers/298633-how-to-find-mean-of-a-vector-including-only-a-specific-range-of-elements#answer_230950

编辑：James Tursa 2016-8-6

在 MATLAB Online 中打开

vector = whatever;
min_value = whatever; % 15 in your example
max_value = whatever; % 25 in your example
x = vector >= min_value & vector <= max_value; % or > and < instead of >= and <=
result = mean(vector(x));

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Stephen23 2016-8-6

在 MATLAB Online 中打开

This is a function, not a script, and you write it just like James Tursa showed you:

function out = fermentationRate(vec,lwr,upr)
out = mean(vec(lwr<vec & vec<upr));
end

and calling it:

>> fermentationRate([20.1, 19.3, 1.1, 18.2, 19.7, 121.1, 20.3, 20.0], 15, 25)
ans =
         19.6

Sandie Nhatien Vu 2016-8-6

编辑：Sandie Nhatien Vu 2016-8-6

Thanks!! Now I finally got the usage of functions and scripts! - and the difference between.

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Answer 2

Star Strider 2016-8-6

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/298633-how-to-find-mean-of-a-vector-including-only-a-specific-range-of-elements#answer_230960

在 MATLAB Online 中打开

This works:

v = [20 8 15 19 7 31];                                                  % Vector
UL = 25;                                                                % Upper Limit
LL = 15;                                                                % Lower Limit
v_mean = sum(v((v >= LL) & (v <= UL))) ./ sum(((v >= LL) & (v <= UL)))  % Mean Of ‘v’ Given Constraints
vm =
      18