How do I use a From Workspace block with table data?

I have an Excel file that contains timestamps in the first column and different measurements in the other columns:

Because it contains date timestamps, the file is not compatible with the "From Spreadsheet" block:

Error encountered in block mdl/From Spreadsheet
Caused by:
First column (time column) must contain numeric values.

After importing the file into my MATLAB base workspace with "readtimetable", and trying to use this variable with a "From Workspace" block, I get:

Invalid variable 'TT' specified as input in 'mdl/From Workspace'. Time must be a Duration vector.

How can I use my spreadsheet as Simulink simulation input?

Answer 1

[MathWorks Support Team]

The "From Workspace" block will only accept time as a duration vector, which is documented here:

https://www.mathworks.com/help/simulink/ug/load-data-using-the-from-workspace-block.html#d126e233497

You can import the Excel data using our Import Tool as 'table' type and then convert the 'table' to a 'timetable':

TT = table2timetable(mySpreadsheet);

Alternatively, you can also directly import the Excel data into a timetable:

TT = readtimetable('mySpreadsheet.xlsx');

Then, convert the timestamps in your timetable into a duration vector by deducting the timestamps from the start time:

TT.Properties.RowTimes = TT.Properties.RowTimes - TT.Properties.StartTime;

Next, you will see this error when you try to run your Simulink model:

Invalid variable 'TT' specified as input in 'mdl/From Workspace'. Timetable for simulation input cannot have more than one variable.

When you load data using a timetable, the timetable must contain data for a single signal, in only one column.

You can create 3 separate timetable variables:

TT1 = removevars(TT,[2 3]);
​​​​​​​TT2 = removevars(TT,[1 3]);
TT3 = removevars(TT,[1 2]);

And add one From Workspace block for each variable TT1, TT2, TT3.

Alternatively, convert the timetable to a timeseries:

ts = timeseries([TT.Var1,TT.Var2,TT.Var3],seconds(TT.Time));

However, note that timeseries are no longer recommended.

See also: https://www.mathworks.com/matlabcentral/answers/1730305-why-do-i-get-a-invalid-variable-error-when-a-time-table-for-simulation-input-has-more-than-one-var