toString function (trying to write a function that takes a cell array expression and returns a string)

Question

Kagome 2011-4-22

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/6040-tostring-function-trying-to-write-a-function-that-takes-a-cell-array-expression-and-returns-a-strin

How do I write a toStringfunction that takes any cell array expression and returns a human-readable string. I need to do this for addition, subtraction, multiplication, division, a number, negation, powers, square roots, and variables. I have the first 4 done but can't seem to figure out the rest. This is what I have so far:

function s = toString(Expr)

type = Expr{1};

switch type

    case {'Add'}
        % the expression looks like {'Add', ___, ___}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' + ' toString(Arg2)];
    case {'Sub'}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' - ' toString(Arg2)];
    case {'Mul'}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' * ' toString(Arg2)];
    case {'Div'}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' / ' toString(Arg2)];
    case {'Num'}
        Arg1 = Expr{2};
        s = [numtostr(Arg1)];
    case {'Neg'}
        Arg1 = Expr{2};
        s = [ '-' toString(Arg1)];
    case {'Pow'}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' ^ ' toString(Arg2)];
    case {'Sqrt'}
        Arg1 = Expr{2};
        s = [toString(Arg1) '^(1/2)'];
    case {'Var'}
        Arg1 = Expr{2};
        s = [toString(Arg1)];
end
end

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Answer 1

Clemens 2011-4-22

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looks you are nearly done.

All I notice is that you always call the toString in all cases but the one with 'Num'. This means in the case 'Var' never a string is created.

You could do this simple by adding:

if ischar(Expr)
  s = Expr;
  return
end

to the beginning. Or maybe in the case 'Var' by not using the toString function - like you did in the 'Num' case.

On a related note - if you plan to create more complicated expressions it might be usefull to add brackets to the strings.

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Kagome 2011-4-22

the not using the toString function for 'Var' made the difference. thank you!

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Answer 2

Kagome 2011-4-22

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https://ww2.mathworks.cn/matlabcentral/answers/6040-tostring-function-trying-to-write-a-function-that-takes-a-cell-array-expression-and-returns-a-strin#answer_8378

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I got it to work with this super long thing lol. Thank you for the input :)!

function s = toString(Expr)

type = Expr{1};

switch type

    case {'Add'}
        % the expression looks like {'Add', ___, ___}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' + ' toString(Arg2)];
    case {'Sub'}
        % the expression looks like {'Sub', ___, ___}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' - ' toString(Arg2)];
    case {'Mul'}
        % the expression looks like {'Mul', ___, ___}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' * ' toString(Arg2)];
    case {'Div'}
        % the expression looks like {'Div', ___, ___}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' / ' toString(Arg2)];
    case {'Num'}
        % the expression looks like {'Num', ___}
        Arg1 = Expr{2};
        s = [num2str(Arg1)];
    case {'Neg'}
        % the expression looks like {'Neg', ___}
        Arg1 = Expr{2};
        s = [ '-' toString(Arg1)];
    case {'Pow'}
        % the expression looks like {'Pow', ___, ___}
        Arg1 = Expr{2};
        Arg2 = Expr{3};
        s = [toString(Arg1) ' ^ ' toString(Arg2)];
    case {'Sqrt'}
        % the expression looks like {'Sqrt', ___}
        Arg1 = Expr{2};
        s = ['sqrt(' toString(Arg1) ')'];
    case {'Var'}
        % the expression looks like {'Var', ___}
        Arg1 = Expr{2};
        s = [num2str(Arg1)];
end
end