Operator '-' is not supported for operands of type 'string'. Matlab

I am looking to use my code to calculate to implement a KNN classifier however I am getting an error when trying to calculate my equation for the Euclidean distance.

I am getting the following error:

Operator '-' is not supported for operands of type 'string'.

Error in A2Q1 (line 18) equation = sqrt((x1-x2)^2 + (y1-y2)^2 + (z1-z2)^2 + (a1-a2)^2 );

Please find the portion of my code with the error below and help me to fix it

while counter <= 13
counter = counter + 1;
x1 = table2array(T([counter],[1]));
y1 = table2array(T([counter],[2]));
z1 = table2array(T([counter],[3]));
a1 = table2array(T([counter],[4]));
**equation = sqrt((x1-x2)^2 + (y1-y2)^2 + (z1-z2)^2 + (a1-a2)^2 );**
result{counter} = equation;

end 
resultcolumn = result';

The equation line is the one causing the error.

Answer 1

[Matt J]

Presumably it is because T contains strings, not numbers.

[Navdeep Singh]

T is an excel file that consists of numbers

[Matt J]

No, T would have to be a variable, not a file. I suggest you attach T in a .mat file so we can examine it together.

[Walter Roberson]

There are circumstances under which when you readtable() an excel file, that a variable can come out as string instead of numeric. In particular it can happen if there are multiple header rows, and it can also happen if one of the columns contains a mix of strings and numbers that happens to start with a number (thus confusing MATLAB into thinking that the first row is not header)