MATLAB: Eliminating unnecessary portions of arrays from structure.

MATLABmatlab data extraction structure array

Hello. I have 1×1574 structure array called "data" with 27 fields. I would like to perform on one of the fields, "IAS". I would like to only extract (take out) the near constant segment, and eliminate the rest. For example.

plot(data(1).Altitude, data(1).IAS)

I get the following graph.

I only want to take out the near constant segment, which is around 300 knots. (Range around plus and minus 10 knots) (From 2.4 * 10^4 to 3.2 * 10^4). When I extract this, I also want this to happen to the other fields.(In other words, I am only interested in the near constant segments of the IAS, and the others are not important).

Now I can do this one by one, but the problem is I have 1574 arrays which is too many. Could anyone help me? Thanks!

Best Answer

If I understand correctly you want something like this

 idx = find(data(1).IAS >= 290 & data(1).IAS <= 310);
 plot(data(1).Altitude(idx), data(1).IAS(idx));

Then you can use 'idx' to extract the desired values from other fields

 data(1).something(idx)

Actually you can also use logical indexing removing 'find'.

Fabio

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data = load('Altitude_Density.txt') ;
altitude = data(:,1) ;
density = data(:,2) ;
plot(altitude,density)

MATLAB: Extracting near constant elements from an array

Your airplane appears to be a jet flying a STAR. When it enters Class C airspace, it is told to slow to 250 kts, then is cleared for the approach and flies the approach at 130 kts.

I didn’t run the code, however it seems to be two 10-element moving average filters to create first ‘x2’ and then ‘meandiffx2’. It then thresholds ‘meandiffx2’ and returns the indices of those values that are <0.25 to ‘constantIndex’. (If it doesn’t find any, the find function will return an empty value. This usually throws an error when concatenated with an existing vector, and will obviously not function as an index in the next line, so I don’t know how the code handles this when it does the ‘constantData.index’ and constantData.data assignments.) It then stores the associated values in the designated structures.

This is a powerful argument for documenting code with comments.

Best Answer

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MATLAB: How to code data in a file onto a plotted graph

MATLAB: Extracting near constant elements from an array

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