Find the average of a column without the use of commands.

I have a matrix that is [365,4] and I need to find the average of each column without the use of commands like mean or size. With the use of a for loop.

[KSSV]

What have you attempted?

[Cappi Nguyen]

I will correct myself by saying that I can use length. But I am running into the problem of using the length command to find the column amount. I am able to use size to find the average.

clear all; close all; clc

A = importdata('la_river.txt');

river = A.data;
R = length(river)
C = length(river(:,))
%%
[R,C] = size(river);
tot = 0.0;
total1 = 0.0;
total2 = 0.0;
total3 = 0.0;
total4 = 0.0;
for c=[1:C]
    for r = [1:R]
   tot = tot + river(r,c);
    end
end

averagetot = tot/(C*R)

for r = [1:R]
    total1 = total1 + river(r,1);
    total2 = total2 + river(r,2);
    total3 = total3 + river(r,3);
    total4 = total4 + river(r,4);
end
   

averagetotal1 = total1/R
averagetotal2 = total2/R
averagetotal3 = total3/R
averagetotal4 = total4/R

Error using importdata
Unable to open file.

[KSSV]

It is problem with importing data. What error you are getting?

[Cappi Nguyen]

Nevermind I am sorry, I realize I could use the size command for this code. But I don't have any errors in the code just needed some help with it.

[dpb]

Beware! length is a dangerous command/function that may not return what you intend -- it is defined as max(size(x)) and so returns either the number of elements in a row or column of any 2D array -- which would depend upon the array configuration. The 4x3 or 3x4 array will both return 4...

Answer 1

[Sai]

Hi Cappi,

I understand that you wanted to calculate the average of columns of a matrix without the usage of in-built commands.

Please find the following code snippet to do the same.

A = [1 2 3;4 5 6;7 8 9;10 11 12] %Consider the matrix for reference

A = 4×3

1 2 3 4 5 6 7 8 9 10 11 12

nRows = height(A);
nColumns = width(A);
avg = zeros(1,nColumns);
for i = 1:width(A)
    C = A(:,i);
    sum = 0;
    for j = 1:nRows
        sum = sum + C(j);
    end
    avg(i) = sum/nRows;
end
disp(avg)

    5.5000    6.5000    7.5000