错误：返回列表中未定义元素编号2

Question

The following function is generating an error.

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

Usage

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

    0.1089181   0.0029240   0.2309942

    error: element number 2 undefined in return list

Can you tell why is it generating an error message?

Answer 1

You are asking too much from the poor function. You want three outputs and it can only deliver one (which is a vector containing three numbers).

• If you want the function to produce the three numbers as separate outputs, declare it as

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

  and remove the line retval = ... at the end.

• If you don't want to modify the function, you need to call it with one output:

   out = select_red(train, test); 

  Then unpack that output into three numbers:

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

  Or the unpacking can be done using a comma-separated list generated from a cell array:

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