How to select with several conditions in a matrix
2 views (last 30 days)
Show older comments
Luisa Andrade
on 23 Nov 2021
Edited: Luisa Andrade
on 25 Nov 2021
I want to select the data from falling below -1 until it turns positive or crosses zero, at least two consecutive times.
An example to clarify what I mean:
In the following matrix I want to selec the bold numbers:
b = [-0.32 -0.5 -1.1 -1.9 -0.5 -0.1 0.2 NaN -1.20 NaN NaN; -0.32 -0.5 -1.1 -1.9 -0.5 -0.1 0.2 NaN -1.20 -0.9 NaN]';
0 Comments
Accepted Answer
Image Analyst
on 23 Nov 2021
See if this is what you want:
b = [-0.32 -0.5 -1.1 -1.9 -0.5 -0.1 0.2 NaN -1.20 NaN NaN; -0.32 -0.5 -1.1 -1.9 -0.5 -0.1 0.2 NaN -1.20 -0.9 NaN]'
[rows, columns] = size(b)
bb = [0 0 0 0 0 0 0 0 0 0 0; 0 0 1 1 0 0 0 0 1 0 0]'
for col = 1 : columns
% Find out where this column is less than -1.
mask = b(:, col) < -1
% Find out the indexes where the runs below -1 start at.
startingIndexes = strfind(mask', [0, 1]) + 1
% Find out where this column is less than 0.
mask2 = b(:, col) < 0
for k = 1 : length(startingIndexes)
index1 = startingIndexes(k);
for row = index1 : rows
if mask2(row)
index2 = row;
else
break; % Went 0 or above so don't increment the second index.
end
end
% Set thos values of bb.
bb(index1:index2, col) = 1;
end
end
bb
4 Comments
Image Analyst
on 24 Nov 2021
Thanks for accepting. Though I was wondering why the last item, where the value is -1.2, you did not want to mark that location as 1. Is it because it did not go positive before it encountered a NaN?
More Answers (0)
See Also
Categories
Find more on Creating and Concatenating Matrices in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!