Clear Filters
Clear Filters

'splitapply' syntax to index multiple columns in a timetable

20 views (last 30 days)
I would like to create a timetable using the split apply function applied to an existing timetable.
testTT = timetable(tmin, duration_min, splitapply(@mean, TT1.I, grp), ...
splitapply(@mean, TT1.KE, grp), ...
splitapply(@sum, TT1.num, grp), ...
splitapply(@mean, TT1.D, grp), ...
splitapply(@sum, TT1{10:1033}), grp));
You can see in the last splitapply command where I'm trying to apply the 'sum' function to 1024 total columns according to the group called 'grp'. I know my syntax is incorrect. But, I also don't know if what I'm trying here is possible (at least the way I'm doing it).
Is there a better approach?
  2 Comments
dpb
dpb on 19 Nov 2021
What is TT1{10:1033} intended to represent, again? The curlies will return an array, not a table which all the dot operations will, but it also lacks a 2D reference--it's only a 1D subscripting expression.
For the above to have any chance, the heights will all have to be the same.
Perhaps you're looking for
splitapply(@sum, TT1(:,10:1033)), grp)
on the last one?
Kelly Kearney
Kelly Kearney on 20 Nov 2021
Unfortunately that syntax isn't valid. You'd need to modify the call to sum to loop over multiple inputs:
% Small sample table
TT1 = array2table(rand(10,5), 'variablenames', {'one','two','three','four','five'});
grp = randi(2, 10, 1);
% One-liner with sum wrapper
testTT1 = array2table(...
splitapply(@(varargin) cellfun(@sum, varargin), TT1, grp), ...
'variableNames', TT1.Properties.VariableNames)
testTT1 = 2×5 table
one two three four five _______ ______ _______ ______ ______ 0.25613 1.6855 0.49839 1.1605 1.032 5.3389 4.5527 1.9127 3.246 4.0721
% Using loops
testTT2 = table;
vname = TT1.Properties.VariableNames;
for ii = 1:length(vname)
testTT2.(vname{ii}) = splitapply(@sum, TT1.(vname{ii}), grp);
end
testTT2
testTT2 = 2×5 table
one two three four five _______ ______ _______ ______ ______ 0.25613 1.6855 0.49839 1.1605 1.032 5.3389 4.5527 1.9127 3.246 4.0721
% The I-wish-it-worked-this-way syntax
testTTbad = splitapply(@sum, TT1, grp);
Error using splitapply (line 132)
Applying the function 'sum' to the 1st group of data generated the following error:

Too many input arguments.

Sign in to comment.

Answers (1)

Kelly Kearney
Kelly Kearney on 19 Nov 2021
Edited: Kelly Kearney on 20 Nov 2021
I really wish splitapply did allow you to pass a table as input and apply the same function to each column of that input. Unfortunately, it doesn't (it will accept table input, but then expects a function that treats each table column as a separate input variable). Instead, a loop is probably the easiest way to do this:
testTT = timetable(tmin, duration_min, splitapply(@mean, TT1.I, grp), ...
splitapply(@mean, TT1.KE, grp), ...
splitapply(@sum, TT1.num, grp), ...
splitapply(@mean, TT1.D, grp));
% Add the summed variables
vname = TT1.Properties.VariableNames(10:1033);
for ii = 1:length(vname)
testTT.(vname{ii}) = splitapply(@sum, TT1.(vname{ii}), grp);
end

Categories

Find more on Data Preprocessing in Help Center and File Exchange

Products


Release

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!