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Synchronizing several large timetables

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Lutetium
Lutetium le 18 Mar 2021
Commenté : Seth Furman le 1 Avr 2021
Dear community,
while I'm waiting for my synchronization to finish, I'm wondering if there is any faster way perform below synchronization. I had to use tall() to avoid running out of memory.
In my example, I have around 19 timetable with timevector and corrsponding signal. I take my first timetable and put it into variable TT1. Then, I put the second table in TT2 and synchronize TT1 and TT2. The resulting table is then transferred into TT1 and I synchronize the next timetable.
While this certainly works, it will take on the current speed (see screenshot below) approx 15 hours or more. Is this a very inefficient way? Is there a way to speed this up significantly? Any obvious mistakes?
I appreciate your input (This is local parallel pool with 16 workers, Xeon E-2286 2.4 GHz, 32 GB RAM)
TT1=tall(tbl{1,1});
for i=2:sigcount
TT2=tall(tbl{1,i});
TTSync=synchronize(TT1,TT2,'union','nearest');
TT1=TTSync;
end
location = 'E:\Matlab\Analysis';
write(location,TT1);
clearvars;

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Seth Furman
Seth Furman le 18 Mar 2021
Where are your timetables coming from? Are you reading them from one or more files? If so, it probably makes more sense to create each tall timetable from a datastore rather than an in-memory timetable. See the link below for an example.
Assuming tblTall is a cell array of tall timetables, we can pass all tall timetables to synchronize at the same time as follows
TTSync = synchronize(tblTall{:,:},'union','nearest');
Please let me know if you are able to try this and, if so, whether you see better performance.
  3 commentaires
Seth Furman
Seth Furman le 1 Avr 2021
It sounds like you are creating a tall cell array of non-tall timetables, e.g.
>> tblCell = {timetable(1,'SampleRate',1),timetable(2,'SampleRate',1)};
>> tblTall = tall(tblCell)
tblTall =
1×2 tall cell array
{1×1 timetable} {1×1 timetable}
>> tblTall{:,:}
Indexing expressions of the form T{...,...} are not supported for tall arrays.
Instead, what you want is to create a non-tall cell array of tall timetables, e.g.
>> tblTall = cellfun(@tall,tblCell,'UniformOutput',false)
tblTall =
1×2 cell array
{1×1 tall} {1×1 tall}
>> tblTall{:,:}
ans =
tall timetable
Time Var1
_____ ____
0 sec 1
ans =
tall timetable
Time Var1
_____ ____
0 sec 2
>> synchronize(tblTall{:,:})
ans =
1×2 tall timetable
Time Var1_1 Var1_2
_____ ______ ______
0 sec 1 2
Please let me know whether you notice any improvement in performance with this workflow.
Seth Furman
Seth Furman le 1 Avr 2021
Please also clarify, does code like the following work on your machine with your timetables or do you get errors about running out of memory?
>> tblCell = {timetable(1,'SampleRate',1),timetable(2,'SampleRate',1)};
synchronize(tblCell{:})
ans =
1×2 timetable
Time Var1_1 Var1_2
_____ ______ ______
0 sec 1 2

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