Cell array in parfor: variable cannot be classified

Question

Florian 2014-10-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/158202-cell-array-in-parfor-variable-cannot-be-classified

评论： Florian 2014-10-10

Hi,

My code looks like this:

allFileFeatures = cell(1,numel(data));
sliced_data_size = round(numel(data)/10);
parfor cpu_id = 1:10
  last_ind = min(cpu_id*sliced_data_size,numel(data));
  first_ind = (cpu_id-1)*sliced_data_size+1;
  sliced_data = data(first_ind:last_ind);
  
  for i = 1:numel(sliced_data)
    %stuff = ...
    
    global_i = cpu_id*sliced_data_size+i;
    allFileFeatures{global_i} = stuff;

I get: "The variable allFileFeatures in a parfor cannot be classified." Google lists a lot of results on this error but I still cannot find the problem in this particular snippet. How can I correct it?

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Answer 1

José-Luis 2014-10-10

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https://ww2.mathworks.cn/matlabcentral/answers/158202-cell-array-in-parfor-variable-cannot-be-classified#answer_154751

编辑：José-Luis 2014-10-10

Your cannot index like that. From the documentation on sliced variables:

Form of Indexing. Within the list of indices for a sliced variable, one of these indices is of the form i, i+k, i-k, k+i, or k-i, where i is the loop variable and k is a constant or a simple (nonindexed) broadcast variable; and every other index is a scalar constant, a simple broadcast variable, colon, or end

Point in case, you cannot define global_i like that. I guess it boils down to the interpreter not being smart enough to see there is no race condition.