Subtract I0 from subsequent timetable values

I have a timetable with different variables corresponding to measurements made with an instrument. One of the variables is a logic variable, "Valve State" that indicates whether the measurement is meant for a background or is a sample measurement.

How could I iterate through the time table and find the most recent variable with "Valve State" == 1 and use that for the calculation on the next chunk of rows which have a "Valve State" == 0?

Answer 1

[Walter Roberson]

measurement(valve_state == 0) = nan;
fillmissing(measurement, 'previous')

[Poison Idea fan]

This works for how I wrote the question, but I wrote the question poorly. I don't need to get rid of the valve_state == 0 values, rather I need to take value(valve_state == 0) - value(valve_state == 1). The values are in a cycle where valve_state == 1 for 10 minutes and then it switches to valve_state == 0 for 30 minutes. When valve_state == 0 I need to use the most recent set of valve_state == 1 for the calculation.

I appreciate the quick response. I am new to Answers.

[Walter Roberson]

If you do

VSR = reshape(valve_state, 1, []);  %need a row
mask = VSR == 0;
start0 = strfind([0 mask], [0 1]);
stop0 = strfind([mask 0], [1 0]);

Now start0(K) marks the start of a run of 0's and stop0(K) marks the end of the same run. Under the assumption that the first datapoint is a 1 rather than 0, you would use the datapoint at start0(K)-1 . So perhaps something like

basevalue = measurement;

if start0(1) == 1
    basevalue(1:stop0(1)) = something;  %this is the case where the valve started 0
    start0(1) = []; stop0(1) = [];
end
for K = 1 : length(start0)
    basevalue(start0(K):stop0(K)) = basevalue(start0(K)-1);
end

[Poison Idea fan]

This is very helpful thank you! I couldn't figure out a way to isolate the run of 0's and what not.