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varfun applied to timetable, how can i keep only 1 of several outputs?

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Yves Haag
Yves Haag on 25 Nov 2020
Answered: dpb on 25 Nov 2020
Hi!
I want to calculate a slope of all columns in a timetable. I apply:
fslope = @(x) polyfit(linspace(1,size(x,1),size(x,1)),x,1) % Slope
like this:
varfun(fslope, X)
what i get is a new timetable with the correct # of columns and rows. However, as polyfit(x,y,1) returns 2 value, those output timetable columns contain two 2 values, which are now grouped. How can i remove one of those (keep only the slope, remove the constant of my polyfit)?
Thanks a lot!

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Accepted Answer

dpb
dpb on 25 Nov 2020
Two ways I see:
Write function that wraps polyfit and only returns the slope instead of using anonymous function. Presuming the above code is already in an m-file script or function this wouldn't be too bad to make a local function within existing file.
Alternatively, just fix up the existing table/timetable -- I happened to have a table already in workspace so
tfit=varfun(@(y) polyfit([1:numel(y)].',y,1),t,'InputVariables',t.Properties.VariableNames(2:end));
tfit=array2table(tfit{1,:}(1:2:end),'VariableNames',tfit.Properties.VariableNames);
Just write over the original table with the retrieved slopes array. The end result of above here was:
>> tfit
tfit =
1×4 table
Fun_P1 Fun_P2 Fun_V Fun_S
______ _______ _____ _______
10 0.59253 1.315 0.11128
>>
With your timetable, use it instead of course. Not sure what you did about the time; don't recall what varfun does with the time in a timetable by default, actually...

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