select a row in a matrix based on jump in value

I have a matrix of data. 9 columns and 5000 rows. The columns represent time series data.

The third column is a variable that comes alive asynchronously. It is an output from a variable that is sampled less frequently than all the others.

I want to keep only those complete rows where this variable changes value.

In practice, the slowly sampled variable is a lab analyser which keeps outputting analogue concentration values which change infrequently. The other variables are temperature readings from an experiment.

Thanks for the help

[Sriram Tadavarty]

Just to get the clarification, you wanted the rows in which third column is alive?

Answer 1

[Ameer Hamza]

Try this. Here M is your 5000*9 matrix

idx = [true; diff(M(:,3)) ~=0];
M = M(idx, :);

[Atique Malik]

Thank you. That works!

[Ameer Hamza]

Glad to be of help.