array processing and sorting

Hello everyone, I have a big problem for my matlab skill level

One of my measuring instruments generates and exports an array like the one below (normally 100+ rows x 5-20 colums) in which each column is in ascending order. Further complication is that often in the last rows there are zeros because in case of different column lengths, a zero-filling process is automatically executed

a =
     1     1     1
     2     3     2
     3     3     4
     5     5     7
     6     9     9
    13    10    15
     0     0    20
     0     0    25

Now if the standard deviation of each row is <=1 then the entire row should be transcribed into a new array, else if standard deviation are >1 the row elements must be split into one or more new lines so that they remain overall anyway ascending sorted. I hope I explained. It is difficult for me to explain even in my language.

In other words I had to get this result

 b =
     1     1     1
     2     3     2
     3     3     4
     5     5     0
     6     0     0
     0     0     7
     0     9     9
     0    10     0
    13     0     0
     0     0    15
     0     0    20
     0     0    25

I will have to import this array into another instrument that can also accept NaN instead of filling with zeros.

thank you in advance

Davide

Answer 1

[Image Analyst]

DId you try std and a for loop?

This looks like a homework problem. If you have any questions ask your instructor or read the link below to get started:

How do I get help on homework questions on MATLAB Answers? - MATLAB Answers - MATLAB Central

Obviously we can't give you the full solution because you're not allowed to turn in our code as your own, but here's a start:

a = [
    1     1     1
    2     3     2
    3     3     4
    5     5     7
    6     9     9
    13    10    15
    0     0    20
    0     0    25];
[rows, columns] = size(a)

rows = 8

columns = 3

sd = std(a, 0, 2)

sd = 8×1

0 0.5774 0.5774 1.1547 1.7321 2.5166 11.5470 14.4338

b = zeros(rows, columns);
for row = 1 : rows
    if sd(row) < 1
        % SD less than 1 so simply transfer the entire row.
        b(row, :) = a(row, :);
    else
        % SD more than 1.  TO DO: Split into separate rows.
    end
end
b

b = 8×3

1 1 1 2 3 2 3 3 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

[Davide Bertelli]

I’m sorry you misunderstood, this is not a homework assignment. Unfortunately, I’m too old to be a student. I am an associate professor in chemistry at the University of Modena and Reggio Emilia in Italy. This is my personal e-mail [e-mail] and here you can find my CV (http://personale.unimore.it/rubrica/dettaglio/bertelli). I usually use Matlab for statistical purpose but in this case I have to transport the results from an instrument to another incompatible one and my skills on array transformation are very very basic.

Best regards

Davide

[Image Analyst]

OK, no problem (75% of people here are students). However, I am not clear on how you want to split up a row with stdev>1 into two or three rows. And I'm not sure how the zeros are to be handled. In the code I gave, of course the zeros are included in the formula for stdev. Do you not want them to be?

[Davide Bertelli]

It’s hard for me to explain it, in trying to do so I insert an image that I hope can clarify the result I need.

I am realizing that the problem is very difficult to solve, because I have a high number of columns and there may be different values that increase SD, and this would require a split in many rows.

Considering that my values are all integer, I thought that a more convenient solution might be to use some fill gaps function with 0 or NaN on each column and then delete all rows which contain only zero.

i.e.

Thank you for help, sorry for my silly questions.

Davide