How to compute the variance of an array progressively taking away the highest values?

Hello,

I have an array of N values, out of which I want to exclude the highest ones. I wanted to visualise how the variance changes by progressively taking a smaller and smaller sample size. The end result would be a plot in which the X-axis represents the amount of individual observations I am taking away, and the Y axis the variance of the remaning data.

I manage to do it, but only by deleting an arbitrary number of N values, which doesn't allow me to create a loop.

Is it possible to loop it?

[Rik]

Do you want to always remove the highest value? If so, you can sort your array and use simple indexing in a for loop.

[Happy_Shovel]

Yep, I was looking for pretty much what Image analyst did in his code! I didn't even know sorting was a thing before today. Thanks to both of you for your answers, you have been super helpful!

Answer 1

[Image Analyst]

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 15;
fprintf('Beginning to run %s.m ...\n', mfilename);

numElements = 20; % Whatever you want.
numbers = 100 * rand(1, numElements);
sortedNumbers = sort(numbers, 'descend');
theVariance = zeros(1, numElements);
for k = 1 : numElements
	theVariance(k) = var(sortedNumbers(k : end));
	fprintf('The variance of the first %d smallest numbers is %f.\n', ...
		numElements - k + 1, theVariance(k));
end
plot(theVariance, 'b.-', 'LineWidth', 2, 'MarkerSize', 20);
xlabel('Number of Elements', 'FontSize', 20);
ylabel('Variance', 'FontSize', 20);
title('Variance as function of number of elements', 'FontSize', 20);
grid on;

[Happy_Shovel]

Thank you so much!