MATLAB Answers


sum every 5 rows of a column, Is the part of code right

Asked by Hamaza24
on 17 Jun 2013

I am trying to sum every 5 rows of a column, Is my part of code right

    instdec = (instdec_t+instdec_d)/2;
    startdec1 = (instdec >= 0.25*overalldec);
    while decpt==1
      for j = 2:npts-4
         startdec2(j) = sum(startdec1(j:j+4));
         if startdec2(j)== 5

I keep getting wrong answers, the second row becomes 2, and everything else is zeros

I would appreciate any support since I am very new to matlab


Jan Simon
on 17 Jun 2013

I've applied a more readable indentation. Now it is obvious that an end is missing.

The purpose of your code is not clearly explained. All we have is the code you have shown here. Then it is impossible to guess, if it satisfies your needs. Please add a detailed description of the aim of the program - by editing the original question, not as comment and not as answer. Thanks.

on 17 Jun 2013

can you provide some example data to test with?



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2 Answers

Answer by Andrei Bobrov
on 17 Jun 2013
Edited by Andrei Bobrov
on 17 Jun 2013
 Accepted answer

startdec2 = sum(reshape([startdec1;zeros(mod(-numel(startdec1),5),1)],5,[])).';


startdec1 = rand(42,1) < .7;
b = conv(startdec1,ones(5,1),'valid');
decpt = find(b == 5,1,'first')-1;


on 17 Jun 2013

I really appreciate you effort Andrei.

and yea jan, if I get you right. decpt 1 and npts is 42

but this way reduces my data as every 5 rows are summed as if I have 42 rows they will be reduced to 9

what I am looking for is to still have the full 42 rows where row 1 will be the sum of rows (1 to 5), row 2 will be sum of rows (2 to 6) and so on. till row 37 (sum of 37 till 42).

it is still bugging me, applying what i learnt from the book is giving me a headache.

please see ADD part in my answer.

on 18 Jun 2013

Thanks I really appreciate it. I worked it out :)

Answer by Hamaza24
on 17 Jun 2013

Hi Jan and tom.

the purpose is to check if the numbers on every row exceed a certain value for a 5 successive rows.

so, the methodology I used is that if the condition of exceeding that certain number happens then generate 1, otherwise 0.

to check the of every five successive rows meet the condition, I want to sum every 5 rows and when the sum is 5 then I know that location and get its original value.

I can't really provide data tom. sorry for that and thanks for your help.


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