Extracting string value from table - Receive error "Expression for initial value of data must evaluate to logical or supported numeric type."

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RockeTruck 2024-5-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2123516-extracting-string-value-from-table-receive-error-expression-for-initial-value-of-data-must-evalua

回答： Tejas 2024-8-14

Test_FaultList.xlsx

Hello,

I'm attempting to extract a char vector from a table, convert it to string, and pass it to another block. Unfortunately, when attempting this I keep running into the error, "Expression 'test_names' for initial value of data 'test_names' must evaluate to logical or supported numeric type." I'm not sure why I keep receiving this error, as I have recreated the same model with a constant set to 1, ran it through a MATLAB function block with simpler code to assign to the output variable (such as "if (u > 0), y = "Greater than 0", else, y = "Less than or equal to 0", and displayed it with a display block, which worked as expected and displayed a string in the display block.

I have attached an example excel file to this post. Please see below for the MATLAB code I am using.

MATLAB script to extract the column from the Excel file (attached):

clear FltDesc
Test_XLRaw=readtable('Test_FaultList.xlsx');
test_names=XLRaw(:,3);

MATLAB code within the function block (test_names scope is set to "Parameter", u scope is set to "Input"):

function y = getFltDesc(u, test_names)
% This function fetches the fault description from the fault list.
% 'u' is the fault number that is an input to this function.
% The function takes u and uses it as a row number and fetches the fault
% description from the 1st column.
y = convertCharsToStrings(test_names{u,["Var3"]});
end

Test Simulink model:

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Answer 1

Tejas 2024-8-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2123516-extracting-string-value-from-table-receive-error-expression-for-initial-value-of-data-must-evalua#answer_1498969

Hello Rocke,

Table-type data cannot be directly passed as an input to a ‘MATLAB Function Block’ in Simulink. The table needs to be converted to a structure-type variable first before it can be accessed by the ‘MATLAB Function Block’. Here is a workaround to access the contents of a table:

Save the table inside a .MAT file.
Create a mask on the ‘MATLAB Function Block’, which includes an edit parameter to store the table and a button with an associated ‘uigetfile’ callback to select the .MAT file. This callback will also be responsible for loading the .MAT file and extracting the table from it.
Associate a mask initialization callback with the edit parameter to convert the table to a structure parameter using the ‘table2struct’ function: https://www.mathworks.com/help/releases/R2022b/matlab/ref/table2struct.html .
This way, the structure parameter will be accessible in the ‘MATLAB Function Block’.