How to concatenate cell array without causing nested cell array

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Nhut Ngo 2019-11-22

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评论： Adam Danz 2019-11-22

I have a matrix years = [2007 2008 2005 2006 2007 2008 2005 2006 2007 2008]. I want to make it a cell array like this years_cell = { [2007 2008] ; [2005 2006 2007 2008] ; [[2005 2006 2007 2008] }. But what I got was 2x1 nested cell array with the first cell as another 2x1 cell array. Thank you for the help in advance guys. Here is my code:

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the cyclist 2019-11-22

编辑：the cyclist 2019-11-22

Is the "rule" that you want to begin a new cell-array element each time a year is earlier than the prior one?

FYI, it's much more useful to paste code, not images of code. Then we can copy/paste into MATLAB if we want to.

Nhut Ngo 2019-11-22

well, I'm working on a project, the variable years changes everytimes. It's not always like that. It depends on the input file.

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Answer 1

the cyclist 2019-11-22

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% Input data
years = [2007 2008 2005 2006 2007 2008 2005 2006 2007 2008];
% Initialize the first cell with the first year
ci = 1;
years_cell = {years(1)};
% Loop over the years
for i = 2:numel(years)
    % If the year is a later one, append to vector in current cell
    if years(i) > years(i-1)
        years_cell{ci} = [years_cell{ci} years(i)];
    else % else increment to next cell and initialize vector with the year
        ci = ci+1;
        years_cell{ci} = years(i);
    end        
end

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Nhut Ngo 2019-11-22

Thank you so much.

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Answer 2

Adam Danz 2019-11-22

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This groups your vector years into groups of monotonically increasing years.

years = [2007 2008 2005 2006 2007 2008 2005 2006 2007 2008]; 
yGrp = cumsum([true,diff(years(:)')<1]); % group ID for increasing years
yearsGrouped = accumarray(yGrp(:),years,[],@(x){x.'}); 

Result

yearsGrouped =
  3×1 cell array
    {1×2 double}
    {1×4 double}
    {1×4 double}
    
celldisp(yearsGrouped)
yearsGrouped{1} =
        2007        2008
yearsGrouped{2} =
        2005        2006        2007        2008
yearsGrouped{3} =
        2005        2006        2007        2008

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Nhut Ngo 2019-11-22

Thank you so much. I'm in an intro class, so cumsum function is something that my teacher has not mentioned yet, so I don't know if I'm allowed to use it.

Adam Danz 2019-11-22

No problem! the cyclist's answer may have more lines but it's actually faster. If you're eager to learn, you could copy my 2-line solution into your code and comment it out until you have time to tear it apart later.

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