Insert time depending on sample time and measurement points into existing table

Question

Robin L 2021-1-21

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https://ww2.mathworks.cn/matlabcentral/answers/722963-insert-time-depending-on-sample-time-and-measurement-points-into-existing-table

评论： Star Strider 2021-1-21

Hello,

I am trying to add time to my existing table. I have tried different methods but I am just getting started with MatLab and can't seem to figure this one out.

Where N = samples = 250.000 and ST = SampleTime = 3 and TS = Timestep = ST/N.

So I want it to add to my 6th column which I have already declared and where row 1 = 0, row 2 = 0 + TS, etc.. until I reach row 250.000 = ST.

Code I wrote for this part:

%add column6 and time to T1
T1.time = rand(250000,1);
ST = 3;             %declare SampleTime
N = 250000;         %SampleSize
TS =  ST/N;    %calc TimeStep
i = 0;
while i < N
  T1(i,6) = 0 + i.*TS;
  i = i + 1;
end

This would give me the error:

"Right hand side of an assignment into a table must be another table or a cell array."

I suppose it has something to do with declaration of which column the data should be placed but I have no idea how I could fix this.

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Answer 1

dpb 2021-1-21

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https://ww2.mathworks.cn/matlabcentral/answers/722963-insert-time-depending-on-sample-time-and-measurement-points-into-existing-table#answer_603013

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In "the MATLAB way", don't use loops where not needed...since you have end points and number, use linspace

ST = 3;             %declare SampleTime
N = 250000; 
T.Var6=linspace(0,ST,N);

You didn't tell us the name for the sixth column, I used the MATLAB default "VarN' form as a placeholder.

Your code has a problem in that you use regular parentheses for assignment where inside the table to write a single value you need {}. It's confusing, I know, but read the section on accessing data in a table; there's a chart that shows all the various addressing modes and what each returns.

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Robin L 2021-1-21

在 MATLAB Online 中打开

Thank you! Much simpler indeed.

This is the code I use now:

ST = 3;                         %declare SampleTime
N = 250000;                     %SampleSize
Tnew=linspace(0,ST,N);          %create linear space
Tnew = array2table(Tnew);       %convert array to table
Tnew = table2cell(Tnew);        %transpose table
Tnew = cell2table(Tnew');
T1 = [T1 Tnew];                 %add Tnew to T1
T1.Properties.VariableNames{'Var1'} = 'Time_s';

Star Strider 2021-1-21

在 MATLAB Online 中打开

Shortcut using Index Matrix Rows and Columns

ST = 3;                         %declare SampleTime
N = 250000;                     %SampleSize
Tnew=linspace(0,ST,N);          %create linear space
T1 = [T1 table(Tnew(:))];       %add Tnew to T1
T1.Properties.VariableNames{'Var1'} = 'Time_s';