Sum of elements in an array over x

Hello all,

I am looking to find the sum of elements in an array which exceed a certain value, e.g. 0.05.

I have this array: [0.023 0.056 0.053 0.034 0.021 0.075 0.088]

As you can see, 4 elements are over 0.05. However, I don't want to know 'how many elements' are over 0.05, I want to find the cumulative sum of the elements which match my criteria.

In this case: 0.056 + 0.053 + 0.075 + 0.088.

Total = 0.272

Can anyone help?

kind regards,

Jacob

[Jacob Merriman]

Just to let people know, I found a way to solve this by simply deleting the elements in the array which were less than 0.05 and creating a new variable. Then we can simply sum the new variable.

[Turlough Hughes]

As a point of clarification, you are looking to add elements where each individual element exceeds a value of 0.05?

Answer 1

[Turlough Hughes]

a =  [0.023 0.056 0.053 0.034 0.021 0.075 0.088];
result = sum(a(a>0.05))

[Turlough Hughes]

You should read up on logical indexing.

[Jacob Merriman]

Amazing, you're a literal star. I will do.

Have a great day.

[Image Analyst]

Not sure how this answers your question. It does not tell you which, and all, sets of elements that sum to more than 0.05 like you asked. If you want that, see my answer below.

[Turlough Hughes]

No problem, you to. I added a follow up comment just to remove any ambiguity.

[Turlough Hughes]

I think the wording is a bit ambiguous and could be interpreted both ways.

Answer 2

[Image Analyst]

In general, this will do it. You need to use combnk() to get all possible combinations of elements added together. Then check the sum of each combination:

v = [0.023 0.056 0.053 0.034 0.021 0.075 0.088]
threshold = 0.05;
counter1 = 1;
counter2 = 1;
rowSum = 0;
for k = 1 : length(v)
	indexes = combnk(1 : length(v), k); % Get all combinations.
	[rows, columns] = size(indexes);
	rowSum = rowSum + rows;
	for row = 1 : rows
                % For this particular combination...
		thisRow = indexes(row, :);
		theSum(counter1) = sum(v(thisRow));
		% See if this sum is more than the threshold
		if theSum(counter1) > threshold
			fprintf('These %d elements sum to more than %.2f\n   ', length(thisRow), threshold);
			fprintf('%.3f + ', v(thisRow(1 : end-1)));
			fprintf('%.3f = %.3f\n', v(thisRow(end)), theSum(counter1));
			counter2 = counter2 + 1;
		end
		counter1 = counter1 + 1;
	end
end
histogram(theSum)
grid on;
caption = sprintf('Histogram of sums after %d combinations', rowSum);
title(caption, 'FontSize', 20);
xlabel('Sum', 'FontSize', 20);
ylabel('Count', 'FontSize', 20);

You'll see 124 (counter2) lines in the command window printing out the sums that are more than your threshold, like these:

These 6 elements sum to more than 0.05

0.023 + 0.056 + 0.034 + 0.021 + 0.075 + 0.088 = 0.297

These 6 elements sum to more than 0.05

0.023 + 0.053 + 0.034 + 0.021 + 0.075 + 0.088 = 0.294

These 6 elements sum to more than 0.05

0.056 + 0.053 + 0.034 + 0.021 + 0.075 + 0.088 = 0.327

These 7 elements sum to more than 0.05

0.023 + 0.056 + 0.053 + 0.034 + 0.021 + 0.075 + 0.088 = 0.350