Matlab: Undefined function 'eq' for input arguments of type 'cell'

Question

This code:

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

returns this error:

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

Why?

you might consider adding matlab as a tag in order to gain visibility to your question. — devlin carnate
– devlin carnate, Commented Jan 12, 2016 at 15:24
What do you expect the if statement to do? prefixTree(1,4).prefixTree2(:,2) looks like that it's a cell array, but your comparison doesn't make any sense at all. In plain English, what is your if statement doing? Take a step backward. — rayryeng
– rayryeng, Commented Jan 12, 2016 at 15:37
the error is specifically pointing to the part where you have prefixTree2(:,2)=='2' Matlab does not allow == for cell comparing, and also '2' would indicate that it is a String type? Try removing the ' ' and see what error it throws? — GameOfThrows
– GameOfThrows, Commented Jan 12, 2016 at 15:38
I expect that if prefixTree(1,4).prefixTree2(:,2) is equal to 2, the code find the unique values in prefixTree(1,4).prefixTree2(:,3). @GameOfThrone i have tried without '' but the code gives me the same error. — cat.cat
– cat.cat, Commented Jan 12, 2016 at 15:43
In which case, I think horchler has got the right answer, which uses strcmp the string compare function that can be applied to indexed cell and compare its content with another string. — GameOfThrows
– GameOfThrows, Commented Jan 12, 2016 at 15:46

horchler · Accepted Answer · 2016-01-12 15:48:53Z

5

The error implies that prefixTree(1,4).prefixTree2(:,2) is a cell array. You can access the individual elements of the second column with prefixTree(1,4).prefixTree2{:,2}. Also, the colon operator implies that there is more than one element in prefixTree(1,4).prefixTree2(:,2) but you're trying to do a scalar comparison. Lastly, you're comparing to a char ('2' as opposed to the number 2) and thus it would be best to use string functions. You can use strcmp to check each element of your cell:

prefixTree(1,4).prefixTree2 = {'1' '2';'3' '2'}; % Example data
strcmp(prefixTree(1,4).prefixTree2(:,2),'2')

Then use any or all to return a scalar for your if statement:

if all(strcmp(prefixTree(1,4).prefixTree2(:,2),'2'))
    ...
end

edited Jan 12, 2016 at 15:48

answered Jan 12, 2016 at 15:41

horchler

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