错误：返回列表中未定义元素编号2

Question

以下功能产生错误。

function [retval] = select_red(train, test)
% shuffle test/data points
  shuffled_test = test(randperm(size(test, 1)), :);

  clubs     = shuffled_test(shuffled_test(:, 1) == 1, :);
  diamonds  = shuffled_test(shuffled_test(:, 1) == 2, :);
  hearts    = shuffled_test(shuffled_test(:, 1) == 3, :);
  spades    = shuffled_test(shuffled_test(:, 1) == 4, :);

  clubs = clubs(1: floor(size(clubs,1)/2),:);
  spades = spades(1: floor(size(spades,1)/2),:);

  shuffled_test = [clubs ; diamonds ; hearts ; spades];

  shuffled_test = shuffled_test(randperm(size(shuffled_test, 1)), :);

  ercf_indep = bayescls(train, shuffled_test, @pdfindep, 0.25 * ones(1,4), 0.1);
  ercf_dep = bayescls(train, shuffled_test, @pdfdep, 0.25 * ones(1,4), 0.1);
  ercf_parzen = bayescls(train, shuffled_test, @pdfparzen, 0.25 * ones(1,4), 0.1);

  retval = [ercf_indep   ercf_dep   ercf_parzen];
endfunction

用法

>> [errindep  errdep  errparzen] = select_red(train, test)
errindep =

    0.1089181   0.0029240   0.2309942

    error: element number 2 undefined in return list

您能说出为什么会生成错误消息吗？

Answer 1

您对功能欠佳的要求太多了。 您需要三个输出，并且只能输出一个（这是一个包含三个数字的向量）。

• 如果希望函数将三个数字作为单独的输出产生，则将其声明为

   [ercf_indep, ercf_dep, ercf_parzen] = select_red(train, test) 

  并在最后删除行retval = ...

• 如果您不想修改该函数，则需要使用一个输出来调用它：

   out = select_red(train, test); 

  然后将输出解压缩为三个数字：

   ercf_indep_out = out(1) ercf_dep = out(2); ercf_parzen = out(3); 

  或者可以使用从单元格数组生成的逗号分隔列表来完成解压缩：

   out_cell = num2cell(out); [ercf_indep_out, ercf_dep, ercf_parzen] = out_cell{:}