MATLAB: Middle Value gets skipped if the length is odd

integer operands are required for colon operator when used as indexMATLAB

Whenever I tried to divide the odd number the middle value get skipped.

Ex:

A = [ 1 0 1 0 1];
len =length(A);
x = [A(1:(len)/2) A(1+(len)/2:len)];

Integer operands are required for colon operator when used as index

I do not know, How to solve this? Anyone could help me.

Best Answer

After you divide the length by 2, you need to use ceil since 5/2 is 2.5 and there is no 2.5 index but ceil(5/2) = 3, which IS the middle index. Try this code:

A = [ 1 0 1 0 1];
len =length(A)  % Not needed -- just for info.
middleIndex = ceil(length(A) / 2)  % Will be 3
% Compute x (though x will be the same as the original according to this formula)
x = [A(1:middleIndex),  A(1 + middleIndex : end)]

It shows:

len =

middleIndex =

x =

1 0 1 0 1

Related Solutions

MATLAB: Write a function fml(x) where given vector x returns first, middle and last. If the number of elements in the vector are even, middle should take the mean value of the innermost elements.

Hello,

Let's take a look at your code,

function [first, middle, last] = fml(x)
%FML Returns the first, middle, and last element of x
first = x(1);
last = x(length(x));
middle = x(length(x))/2;
if mod(length(x),2)==1
    middle = (x(length(x)/2+1)+x(length(x)/2-1))/2;
elseif mod(length(x),2)==0
    middle = x(length(x))/2;
end

Your computation of first and last seems to be good; however, there is a problem with your computation of middle. First, you don't need the line,

middle = x(length(x))/2;

as you will assign a different value to middle anyways.

Next, let's consider your code,

if mod(length(x),2)==1
    middle = (x(length(x)/2+1)+x(length(x)/2-1))/2;
elseif mod(length(x),2)==0
    middle = x(length(x))/2;
end

Here you are checking if the length is odd or even using modulus then determining the value of middle based on that. However, you have two problems:

1) if mod(length(x),2) == 1, we know the length is odd, meaning that,

middle = (x(ODD/2+1)+x(ODD/2-1))/2;

ODD/2 will produce a something and 1/2 result, which is not a valid index. Furthermore, if it has an odd length, then we know that it does in fact have a middle value [1 2 3] has middle value 2 for example. Try changing the line to,

middle = x(ceil(length(x)/2));

Then, when the modulus = 0, we know it's even, so try using the line,

middle = (x(length(x)/2) + x(length(x)/2+1))/2;

I hope this helps!

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

Like this:

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

Best Answer

Related Solutions

MATLAB: Write a function fml(x) where given vector x returns first, middle and last. If the number of elements in the vector are even, middle should take the mean value of the innermost elements.

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

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