MATLAB: How to find the index of a randomly chosen element of an array

find

Would anyone suggest me the code of finding out the index of a randomly selected element of an array or matrix?

For example, after randomly selecting an element from 'a', I want to find out the index number of the chosen element. This index number should be a variable as each time i randomly select an element, the corresponding index number of the selected element may change.

a = [4 5 10 15 20];

Best Answer

Try this

idx = find(a==random_element)

Related Solutions

MATLAB: Random matrix with maximum values.

You could do this:

w = floor(sqrt(30))
rows = 1 : w
counter = 1;
for k = 1 : length(rows)
	columns(k) = floor(30/rows(k));
	for col = 1 : columns(k)
		fprintf('For %d rows, and %d columns, there are %d elements.\n',...
			rows(k), col, rows(k) * col);
		allMatrices{counter} = rand(rows(k), col);
		counter = counter + 1;
	end
end

You'll get every possible matrix size with 30 or fewer elements in it. And each one will be a cell in the allMatrices cell array. It has to be a cell array rather than a 3-D matrix because the matrices are not all the same size. You'll see in the command window:

w =

rows =

1 2 3 4 5

For 1 rows, and 1 columns, there are 1 elements.

For 1 rows, and 2 columns, there are 2 elements.

For 1 rows, and 3 columns, there are 3 elements.

For 1 rows, and 4 columns, there are 4 elements.

For 1 rows, and 5 columns, there are 5 elements.

For 1 rows, and 6 columns, there are 6 elements.

For 1 rows, and 7 columns, there are 7 elements.

For 1 rows, and 8 columns, there are 8 elements.

For 1 rows, and 9 columns, there are 9 elements.

For 1 rows, and 10 columns, there are 10 elements.

For 1 rows, and 11 columns, there are 11 elements.

For 1 rows, and 12 columns, there are 12 elements.

For 1 rows, and 13 columns, there are 13 elements.

For 1 rows, and 14 columns, there are 14 elements.

For 1 rows, and 15 columns, there are 15 elements.

For 1 rows, and 16 columns, there are 16 elements.

For 1 rows, and 17 columns, there are 17 elements.

For 1 rows, and 18 columns, there are 18 elements.

For 1 rows, and 19 columns, there are 19 elements.

For 1 rows, and 20 columns, there are 20 elements.

For 1 rows, and 21 columns, there are 21 elements.

For 1 rows, and 22 columns, there are 22 elements.

For 1 rows, and 23 columns, there are 23 elements.

For 1 rows, and 24 columns, there are 24 elements.

For 1 rows, and 25 columns, there are 25 elements.

For 1 rows, and 26 columns, there are 26 elements.

For 1 rows, and 27 columns, there are 27 elements.

For 1 rows, and 28 columns, there are 28 elements.

For 1 rows, and 29 columns, there are 29 elements.

For 1 rows, and 30 columns, there are 30 elements.

For 2 rows, and 1 columns, there are 2 elements.

For 2 rows, and 2 columns, there are 4 elements.

For 2 rows, and 3 columns, there are 6 elements.

For 2 rows, and 4 columns, there are 8 elements.

For 2 rows, and 5 columns, there are 10 elements.

For 2 rows, and 6 columns, there are 12 elements.

For 2 rows, and 7 columns, there are 14 elements.

For 2 rows, and 8 columns, there are 16 elements.

For 2 rows, and 9 columns, there are 18 elements.

For 2 rows, and 10 columns, there are 20 elements.

For 2 rows, and 11 columns, there are 22 elements.

For 2 rows, and 12 columns, there are 24 elements.

For 2 rows, and 13 columns, there are 26 elements.

For 2 rows, and 14 columns, there are 28 elements.

For 2 rows, and 15 columns, there are 30 elements.

For 3 rows, and 1 columns, there are 3 elements.

For 3 rows, and 2 columns, there are 6 elements.

For 3 rows, and 3 columns, there are 9 elements.

For 3 rows, and 4 columns, there are 12 elements.

For 3 rows, and 5 columns, there are 15 elements.

For 3 rows, and 6 columns, there are 18 elements.

For 3 rows, and 7 columns, there are 21 elements.

For 3 rows, and 8 columns, there are 24 elements.

For 3 rows, and 9 columns, there are 27 elements.

For 3 rows, and 10 columns, there are 30 elements.

For 4 rows, and 1 columns, there are 4 elements.

For 4 rows, and 2 columns, there are 8 elements.

For 4 rows, and 3 columns, there are 12 elements.

For 4 rows, and 4 columns, there are 16 elements.

For 4 rows, and 5 columns, there are 20 elements.

For 4 rows, and 6 columns, there are 24 elements.

For 4 rows, and 7 columns, there are 28 elements.

For 5 rows, and 1 columns, there are 5 elements.

For 5 rows, and 2 columns, there are 10 elements.

For 5 rows, and 3 columns, there are 15 elements.

For 5 rows, and 4 columns, there are 20 elements.

For 5 rows, and 5 columns, there are 25 elements.

For 5 rows, and 6 columns, there are 30 elements.

MATLAB: Get the column number of the false values in a logical output

You can use the find function:

N = 50;
A = 1:N;
B = 1:41;
index = ismember(A,B);
[row,col] = find(~index);
disp(col)
    42    43    44    45    46    47    48    49    50

Best Answer

Related Solutions

MATLAB: Random matrix with maximum values.

MATLAB: Get the column number of the false values in a logical output

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