Remove rows in a matrix where there isn't a change larger than 3 in either column

I have a 225x2 matrix where the first 200 rows or so (it varies by data set) does not change by more than 3 in either column. I need a function to delete all of the rows where there isn't a change greater than 3 and then condense the matrix.

Answer 1

[Image Analyst]

Do you mean a change between the first column and second column in each row?

Try this

changes = m(:, 2) - m(:, 1); % Change from col 1 to col 2.
rowsToDelete = changes > 3;
m = m(~rowsToDelete, :);

[Michael Sposato]

No between each row of data. For example the matrix might look something like this:

1000 520

1000 521

1001 519

800 250

324 104

I want to delete the whole row in the matrix when either column doesn't change by more than 3 from the previous row.

[Dyuman Joshi]

In the example you mentioned, both columns in the 2nd row don't change by more than 3 from the 1st row.

Now, do you want to remove the 2nd row, and compare the 3rd row to the first? Or do you want to compare the 3rd row to the 2nd one?

[Image Analyst]

You forgot to give the output. Is the first row to be deleted too? Or just the second and third row?

m = [...
    1000    520
    1000    521   
    1001    519
    800    250
    324    104];
changes = diff(m, 1) % Change from one row to the next

changes = 4×2

0 1 1 -2 -201 -269 -476 -146

rowsToDelete = [0; any(changes >= 0 & changes < 3, 2)]

rowsToDelete = 5×1

0 1 1 0 0

m = m(~rowsToDelete, :)

m = 3×2

1000 520 800 250 324 104