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

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!

Answer 1

[dpb]

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...