MATLAB: Turning x amount of data points in to 100 to get a percentage

gaitkinematicspercentage

Hi,

I have a row vector containing 120 data points. How would I convert that data in to 100. I am working on gait cycles and would like to analyse the knee angles at a certain percentage of the cycle. This is what I was attempting to use but that just seems to ignore any data points past the 100th value.

y = linspace(1,100,100); Gait_Cycle_Percent =interp1(x,y) where x is the raw 120×1 data.

Thank you

Best Answer

If you have the signal processing toolbox:

https://se.mathworks.com/help/signal/ref/resample.html

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MATLAB: Normalize different size arrays to all be 100 points long with resample

Using resample (or any other interpolation method, although resample is best for signal processing applications) to get the same number of data for each subject risks having a different sampling frequency for each subject. This also means that any signal processing you do (such as filtering) would have to be individualised for each subject, as would subsequent data analysis. So I would advise against that.

You could likely do it by using the ‘p’ and ‘q’ parameters as the integer values of the actual and desired record lengths, since resample just needs those values to change the sampling frequency (and record length) of the argument vector. (It cares not one whit what the numbers actually represent.) However for the reasons I already mentioned, this is unadvisable.

Use cell arrays to store the varying-length records, with the same sampling frequency for all of them, and then use the same analytical techniques for every subject.

MATLAB: Turning data in time domain into percentage

I'm guessing your time column represent a portion of the day (ie, hh:mm) and it's that column that you want to turn into a percentage.

datestr(mot1.time(1:5))
ans =
  5×8 char array
    ' 6:36 AM'
    ' 6:47 AM'
    ' 7:00 AM'
    ' 7:12 AM'
    ' 7:23 AM'

in which case, they already are a percentage. Do you want to scale them from 0:100 instead of 0:1? It may be better to leave them in their original form if you want to use them as datetime values. But here's how to scale them to 0:100

mot1.time = mot1.time*100    % or mot1.time = round(mot1.time*10)
mot1.time(1:5)
ans =
         27.5
       28.333
       29.167
           30
       30.833

If you want actual '%' symbols you'd have to convert them to strings | char arrays

mot1.time = strcat(num2str(round(mot1.time*100)),'%')
%or 
mot1.time = cellstr(strcat(num2str(round(mot1.time*100)),'%'))

But again, they would be virtually worthless in that form if you're planning on using them for analysis.

If you need them as lables, you can always add an additional column to the table.

Best Answer

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MATLAB: Normalize different size arrays to all be 100 points long with resample

MATLAB: Turning data in time domain into percentage

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