使用分类协变量回归matlab错误

Question

我正在尝试运行以下示例： http://nl.mathworks.com/help/stats/group-comparisons-using-categorical-arrays.html

使用Matlab R2013b。

clear
load('carsmall')
cars = table(MPG,Weight,Model_Year);
cars.Model_Year = nominal(cars.Model_Year);
fit = fitlm(cars,'MPG~Weight*Model_Year')

不幸的是我收到了错误：

Error using classreg.regr.FitObject/assignData (line 257)
Predictor and response variables must have the same length.

Error in classreg.regr.TermsRegression/assignData (line 349)
            model = assignData@classreg.regr.ParametricRegression(model,X,y,w,asCat,varNames,excl);

Error in LinearModel.fit (line 852)
            model = assignData(model,X,y,weights,asCatVar,dummyCoding,model.Formula.VariableNames,exclude);

Error in fitlm (line 111)
model = LinearModel.fit(X,varargin{:});

有什么线索？