How to interpolate data with different sample times

Question

Paul 2024-9-3，14:14

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回答： Star Strider 2024-9-3，15:08

I'm trying to align two structures such that I can subtract one from the other. Right now this isn't possible due to struct A being longer than Struct B, and we know that two structs need to be the same length to perform operations like subtracting. These structures have a field for time (in datenum format) and a field for value (lets say units of Watts)

The data I'm dealing with is for an entire day (00:00 to 23:59) and the sample times of the two data structs are roughly 50ms. To be exact Struct A has a sample time of 50.06ms according to my calculation and Struct B has a sample time of 50.01ms.. So for a 24hr period for Struct A there are 1723428 samples with a corresponding datenum value, and for Struct B there are 1709086 samples with a corresponding datenum value.

My question is how can I interpolate Struct B such that there are the same amount of samples as Struct A, allowing me to perform the subtraction I want, but without compromosing the data. I'd like to add data points at evenly spaced intervals so that it doesn't mess up anything, Thanks :)

StructA:

StructB:

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Answer 1

dpb 2024-9-3，14:50

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在 MATLAB Online 中打开

Two basic choices

resample in the Signal Processing TB will let you simply resample B by the ratio of the sizes with a phase-maintaining filtering operation...

B.newValue=resample(B.value,numel(A.value),numel(B.value));

or use interp1 and the time data from A

B.newValue=interp1(B.time,B.value,A.time);

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Answer 2

Star Strider 2024-9-3，15:08

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‘These structures have a field for time (in datenum format) and a field for value (lets say units of Watts)’

I would create them as timetable arrays (it would be easier to convert the datenum values to datetime arrays first, and put those into a table or directly into a timetable) and then use the retime function with an appropriatee ‘dt’ value (the 'TimeStep',dt name-value pair) to create arrays of the same size sampled at the same times. Another option could be to use the synchronize function.

I believe all these are available in R2021b, however I don’t remember exactly when the various options were introduced.