Unrecognized function or variable 'sum'.

Question

Yao Yuan Xie 2022-9-27

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1812755-unrecognized-function-or-variable-sum

回答： Steven Lord 2022-9-27

采纳的回答： Chunru

classdef question2

methods

function q2a = l1qa(~,table)

clear sum;

z = zeros(height(table),2);

for i = 2:height(table)

z(i,1) = i;

temp = table(i,3:6);

z(i,2) = sum(temp{:,1:4});

%z(i,2) = temp{1,1} + temp{1,2} + temp{1,3} + temp{1,4};

end

[sum,index] = max(z(:,2));

table(index,1)

output = "Name: " + table{index,1} + newline +"Mark: " + sum;

q2a = output;

end

opts = detectImportOptions('course_grades_2022.xlsx');

opts = setvartype(opts, {'ID_Number', 'Name'}, 'string');

table = readtable('course_grades_2022.xlsx', opts);

g = question2();

g.l1qa(table)

Unrecognized function or variable 'sum'.

Error in question2/l1qa (line 10)

z(i,2) = sum(temp{:,1:4});

Error in test1 (line 6)

g.l1qa(table)

This is the error I'm getting after trying to implement my code as a function in a class. It seems that matlab is trying to evaluate sum as a variable instead of a function. I have tried clearing sum but it does not fix the problem. I am new to matlab and any help would be appreciated.

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Answer 1

Chunru 2022-9-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1812755-unrecognized-function-or-variable-sum#answer_1061395

编辑：Chunru 2022-9-27

classdef question2
    
    methods
        function q2a = l1qa(~,table)
            % clear sum;            
            s = 0;              % don't use the function name as variable
            z = zeros(height(table),2);
            for i = 2:height(table)
                z(i,1) = i;
                temp = table(i,3:6);
                z(i,2) = sum(temp{:,1:4});
                %z(i,2) = temp{1,1} + temp{1,2} + temp{1,3} + temp{1,4};
                
            end
            %[sum,index] = max(z(:,2));
            [s,index] = max(z(:,2));
            table(index,1)
            
            % output = "Name: " + table{index,1} + newline +"Mark: " + sum;
            output = "Name: " + table{index,1} + newline +"Mark: " + s;
            q2a = output;
        end
    end
end
opts = detectImportOptions('course_grades_2022.xlsx');
opts = setvartype(opts, {'ID_Number', 'Name'}, 'string');
table = readtable('course_grades_2022.xlsx', opts);
g = question2();
g.l1qa(table)

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Answer 2

Steven Lord 2022-9-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1812755-unrecognized-function-or-variable-sum#answer_1061710

It seems that matlab is trying to evaluate sum as a variable instead of a function.

That is correct, because in the method it is a variable. Looking at part of your code:

        function q2a = l1qa(~,table)
            clear sum;
            z = zeros(height(table),2);
            for i = 2:height(table)
                z(i,1) = i;
                temp = table(i,3:6);
                z(i,2) = sum(temp{:,1:4});
                %z(i,2) = temp{1,1} + temp{1,2} + temp{1,3} + temp{1,4};
                
            end
            [sum,index] = max(z(:,2));

On this line of code you assign a value to the variable sum. That means that in this function the identifier sum must be a variable. Your use in the for loop is therefore an attempt to index into that variable before it's actually defined.

You cannot use the same identifier as both a variable and a function in the same function, even if you refer to that identifier before you create the variable. Clearing the variable won't change the fact that MATLAB saw the assignment to the variable when it parsed the code and so decided at that time that sum is a variable in this function.

I'd recommend changing the name of your variables sum (so it doesn't conflict with the sum function) and table (which already has a meaning in MATLAB.)