I need help finding the center of an n * n array. TA couldn't figure it out

Assign middleElement with the element in the center of squareArray. Assume squareArray is always an n x n array, where n is odd. Hint: elementIndex should be rounded to an integer. Ex: If squareArray is [1, 2, 3; 4, 5, 6; 7, 8, 9], then middleElement is 5.

function middleElement = FindMiddle(squareArray) 
% FindMiddle: Return the element in the center of squareArray
%   Inputs: squareArray - n x n input array, where n is odd
%
%   Outputs: selectedData - center element of squareArray

      % Assign elementIndex with location of middle row/col
      % Hint: Use the size() function to deterimine the dimension of squareArray
      elementIndex = size(squareArray); %3.5 /2

      % Assign middleElement with the center element of squareArray
      middleElement = squareArray(elementIndex);
  end

[Jan]

@Jose Garcia: You have set a flag with the contents: "Gives the wrong answer when inputting values". It is not clear, which code you mean and what you observe. Please post a comment and add details. The flags are thought to inform admins and editors about messaged, which might violate the terms of use, e.g. if they are rude or spam.

Answer 1

[Image Analyst]

Like this:

m = [1, 2, 3; 4, 5, 6; 7, 8, 9]
middleElement = m(ceil(numel(m)/2))

[Image Analyst]

An alternate way is this:

m = [1, 2, 3; 4, 5, 6; 7, 8, 9]
middleIndex = ceil(size(m, 1)/2)
middleElement = m(middleIndex, middleIndex)

Assumes that m is square, unlike the more robust first method I gave you.

[Blair Hall]

That works for finding five in that array but I need it to also work for:

Check if FindMiddle([1, 2, 3, 4, 5; 6, 7, 8, 9, 10; 11, 12, 13, 14, 15; 16, 17, 18, 19, 20; 21, 22, 23, 24, 25;]) returns 13 Function failed for input: [1 2 3 4 5;6 7 8 9 10;11 12 13 14 15;16 17 18 19 20;21 22 23 24 25] Expected: 13 Your value: 5

[Rik]

You must have made a mistake in copying, because this code works for the matrix you mention.

You could even do it in an overpowered way (equivalent to the first method by Image Analist):

center_loc=num2cell(ceil(size(m)/2));
m(sub2ind(size(m),center_loc{:}))
%equivalent to m(center_loc{1},center_loc{2},...,center_loc{n})

[Rik]

And did you already follow the advice of doing the Matlab Onramp tutorial?

[Ian Connor]

middleElement = squareArray(ceil(numel(squareArray)/2))

[Image Analyst]

Yes, that was my first answer. You just replaced m with squareArray - a simple variable name change.

Blair must have done something wrong because the cases he gave all work beautifully with this code:

% Case 1.  Returns 5.
m = [1, 2, 3; 4, 5, 6; 7, 8, 9]
middleValue = FindMiddle(m) 

% Case 2.  Returns 13.
m = [1, 2, 3, 4, 5; 6, 7, 8, 9, 10; 11, 12, 13, 14, 15; 16, 17, 18, 19, 20; 21, 22, 23, 24, 25]
middleValue = FindMiddle(m) 

% Case 3.  Like Case 2 but without commas. Returns 13.
m = [1 2 3 4 5;6 7 8 9 10; 11 12 13 14 15; 16 17 18 19 20;21 22 23 24 25]
middleValue = FindMiddle(m) 

function middleElement = FindMiddle(m)
	% Method 1:
	middleIndex = ceil(size(m, 1)/2);
	middleElement = m(middleIndex, middleIndex);
	% Method 2: (Commented out now)
	% middleElement = m(ceil(numel(m)/2))
end

[Alejandro Alarcon]

I tried this answer but MATLAB does not recognize squareArray function

[Rik]

That's because it isn't a function, it's a variable.

[Image Analyst]

My answer does not have the word squareArray in it, so you didn't try my answer. Again, here is the complete solution:

% Case 1.  Returns 5.
m = [1, 2, 3; 4, 5, 6; 7, 8, 9]
middleValue = FindMiddle(m) 

% Case 2.  Returns 13.
m = [1, 2, 3, 4, 5; 6, 7, 8, 9, 10; 11, 12, 13, 14, 15; 16, 17, 18, 19, 20; 21, 22, 23, 24, 25]
middleValue = FindMiddle(m) 

% Case 3.  Like Case 2 but without commas. Returns 13.
m = [1 2 3 4 5;6 7 8 9 10; 11 12 13 14 15; 16 17 18 19 20;21 22 23 24 25]
middleValue = FindMiddle(m) 

function middleElement = FindMiddle(m)
	% Method 1:
	middleIndex = ceil(size(m, 1)/2);
	middleElement = m(middleIndex, middleIndex);
	% Method 2: (Commented out now)
	% middleElement = m(ceil(numel(m)/2))
end

If you want to replace m in FindMiddle, you can. I changed it to m since my code works for any size matrix, not just square ones.

Answer 2

[Mandy Downs]

function middleElement = FindMiddle(squareArray) 
% FindMiddle: Return the element in the center of squareArray
%   Inputs: squareArray - n x n input array, where n is odd
%
%   Outputs: selectedData - center element of squareArray
    
    % Assign elementIndex with location of middle row/col
    % Hint: Use the size() function to deterimine the dimension of squareArray
    elementIndex = size (squareArray);
    elementIndex = (elementIndex / 2) + 0.5;
    
    % Assign middleElement with the center element of squareArray
    middleElement = squareArray (elementIndex, elementIndex);
    middleElement = middleElement (1)
    
end

[Patricio]

Thank you