Pre allocate memory for unknown variable size

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Ricky 2013-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/76612-pre-allocate-memory-for-unknown-variable-size

Hello Everyone,

I have a cell array whose dimensions are 1000*1 . These are sensor scans from a laser and always I get a cell array with above dimensions. When the sensor is ON the data gets stored in the above cell array.

So for example in trial 1 laser sensor is ON for 5 seconds then the cell array has data in only first 180 cells,the rest of the cells are empty. In the trial 2 laser sensor maybe ON for 6 seconds and I can get data in 200 cells.

Currently I am using a for loop to iterate through the cell array and check and store data for non-zero elements. But this reduces speed of my code as I am not able to pre allocate memory.

Can anyone suggest an alternative method.

Regards

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Jan 2013-5-22

Please post the code you use. Otherwise it is hard to suggest improvements. Perhaps a cellfun('isempty', C) is sufficient already, or an extra list of occupied indices.

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Answer 1

Iain 2013-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/76612-pre-allocate-memory-for-unknown-variable-size#answer_86259

Preallocate to the largest size you will ever need, and for the unused elements, you can set them to a known bad value. eg. NaN, Inf, -Inf, or clear those elements with:

Returned(57:end) = [];