Adding multiple rows in Array

Question

I have an array A size of 16X16 and I want to add first 3 rows out of 16 in A. What is the most efficient solution in MATLAB?

I tried this code but this is not efficient because I want to extend it for large arrays:

filename = 'n1.txt';
B = importdata(filename);
i = 1;
D = B(i,:)+ B(i+1,:)+ B(i+2,:);

For example, if I want to extend this for an array of size 256x256 and I want to extract 100 rows and add them, how I will do this?

Community · Accepted Answer · 2017-05-23 11:59:02Z

5

A(1:3,:);%// first three rows.

This uses the standard indices of matrix notation. Check Luis's answer I linked for the full explanation on indices in all forms. For summing things:

B = A(1:100,:);%// first 100 rows
C = sum(B,1);%// sum per column
D = sum(B,2);%// sum per row
E = sum(B(:));%// sum all elements, rows and columns, to a single scalar

edited May 23, 2017 at 11:59

CommunityBot

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answered Nov 4, 2015 at 16:32

Adriaan

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1 Comment

rayryeng Over a year ago

@ShahFahd I edited your original question because there were many syntax errors and it wouldn't run as is. I also removed a lot of the superfluous code to get to the root of your problem. It wasn't me who wrote you the answer. Adriaan did.

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