How to calculate the sum of particular row in a matrix??

I have a large matrix A with the dimension 1024 X 256. I want to add the elements of the 104th row from column 25 to 75. I tried this code but it doesn't work. Can someone please guide me on this?

B= sum(A(104, 25:75)

Answer 1

[Star Strider]

To sum across a row, specify dimension 2:

B= sum(A(104, 25:75),2)

That should do what you want.

[Bibek Dhami]

Thank you it worked. Actually I was missing the dimension 2.

[Star Strider]

My pleasure!

I noticed the missing dimension argument, and corrected it.

If my Answer helped you solve your problem, please Accept it!

.

[Bibek Dhami]

Once again thank you. I am not sure where I am messing up in this code I have written.

Let me make you clear what I am doing. I have 400 files in the folder named spectra. I need to process each of these files to get the value( I need to sum over the above- mentioned rows and get a value). Then I need to create the 20 X20 matrix out of these values.

Why am I not getting this matrix named int_750? It only shows zeros as the elements rather than the values.

F = dir('C:\Users\bdham001\Desktop\Spectra\*.exe') ;
   
val_750= zeros(1,400);
for i = 1:length(F)
      file = load(F(i).name);
      val_750(1,i)=sum(file(800,1:end),2);
end
   

int_750= zeros(20);
for i = 1:1:20
    for j = 1:1:20
        if mod(i, 2) == 0
           int_750 (i, j) = val_750(1, 20*(i-1)+j);
        else
            int_750(i, j) = val_750(1, 20*i-(j-1));
        end
    end
end  



B= int_750

[Star Strider]

Difficult to say.

One problem is that using load with a .mat file into a variable (that is generally considered to be good programming practice, so no problem there), loads into a structure. It is then necessary to extract the data from the structure. (Using load with a text file simply loads the numeric data in the text file, providing it is a compatible text file.)

However, here the code uses load with ‘.exe’ files, and I have absolutely no idea what the ‘file’ variable then contains.

Determining what the ‘.exe’ files contain and what they load into ‘file’ is obviously your next project.

[Bibek Dhami]

I cannot open this file directly so I converted it into text file and uploaded. It actually contains the numeric value

[Star Strider]

Using load with that file produces a (1024x256) double array. Taking the sum across row 800 produces a value of 206685.

I cannot determine what the problem is with the code. First, check to see what ‘F’ contains. Then see what ‘F(i).name’ is, and then what is in ‘file’. That is the only way I can think of to troubleshoot this.

[Bibek Dhami]

If I individually perform these operations, I can get the value. But I have 400 such files in the folder and I need these 400 values as you obtained for this particular file(206685). That's why I am trying to use for loop in the first case.

[Star Strider]

I understand.

The problem is that my ability to help you with the file problem is significantly limited. That is the reason that I encourage you to determine what is in ‘F’ before the loop and in each iteratiion, and what is in ‘file’ in each iteration. You simply need to list ‘F’ to determine what it is, and list every value of ‘F(i).name’, at least for the first few (perhaps 10) iterations, until the first loop works as you want it to work. One way to determine what is in ‘file’ is to use the size and nnz functions to see what is in it.