Undefined function 'eq' for input arguments of type 'cell'.

Hi! I don't understand because my code gives an error

 if (prefixTree(1,4).prefixTree2(:,2)=='2')
 unique(prefixTree(1,4).prefixTree2(:,3))
 end

Error:

Undefined function 'eq' for input arguments of type 'cell'.

Thanks

Answer 1

[Stephen23]

Relational operators can be used with numeric arrays or character arrays. It makes no sense to use them with cell arrays. Consider the following:

>> {3}==3 % cell array
Undefined function 'eq' for input arguments of type 'cell'. 
>> 3==3   % numeric array
ans =
     1

if you wish to test for a particular string, use strcmp:

>> strcmp('3','3')
ans =
     1
>> strcmp({'3'},'3')
ans =
     1

Here some of the other questions asked by people trying to perform numeric operations on cell arrays (which is always an error, as numeric operations can only be performed on numeric arrays):

http://www.mathworks.com/matlabcentral/answers/49180-error-undefined-function-plus-for-input-arguments-of-type-cell

http://www.mathworks.com/matlabcentral/answers/218421-how-to-make-a-string-one-string-in-a-cell-array

http://www.mathworks.com/matlabcentral/answers/225920-double-vs-cell-undefined-function-plus-for-input-arguments-of-type-cell

http://www.mathworks.com/matlabcentral/answers/254754-what-can-this-error-mean-undefined-function-ge-for-input-arguments-of-type-cell-error-in-hw6

http://www.mathworks.com/matlabcentral/answers/56751-undefined-function-times-for-input-arguments-of-type-cell