Concatenate integer to variable name

Question

Ioannis Agalliadis 2017-6-29

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回答： Steven Lord 2017-6-30

Hi, I would like to concatenate the number of the corresponding level to the cell arrays I create. This is what I have tried so far along with other things but nothing seems to work.

for j= 1:230
      for i=1:8
          for lvl = 3:5
             strcat([haar_decomp_ext{j,i}, haar_coeff_num_ext{j,1}],lvl) = wavedec(Ext{j}(:,i+1),lvl,'haar');
          end
      end
end

Thanks in advance.

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dpb 2017-6-29

编辑：dpb 2017-6-29

Depends on what you need to do with it...which you've not provided sufficient information about to know, precisely.

But, with the same number of columns, presuming they're all numeric, then a double 2D array will hold them all which is the simplest storage mechanism and therefore fastest and most memory efficient. If your case is to process all, then single expressions over that array compute things like averages or math expressions directly on all elements in a single expression.

If it is needed to process each of these subsets somehow individually, then once you've processed a set is there any reason to keep it in memory any longer or just the result? If the former, then still a 2D array is most efficient; simply save the result(s) before bringing in the next.

You can, of course, create a cell array that contains each of these 2D arrays as one of its elements, but to do that just make an array, don't create new numbered variables. Or, you could, as the reference documentation shows, use structures or a more recent alternative of the table. In a table you could/would create an additional grouping variable for each of the subsets that could be use to do calculations by each.

There are many choices; which is best depends on what objective is, but none use sequentially-named variables. That isn't to say there aren't places where eval has it uses but this is not one of those... :)

Ioannis Agalliadis 2017-6-30

编辑：Ioannis Agalliadis 2017-6-30

Every column belongs to a different channel and I have 8 columns of them. The first column is the time. The number of rows is different because the time of the movement that I am investigating varies. That means, that I have a variable number of rows always. Now, as I see that storing these data to cell arrays would make the work more difficult I was wondering what if I joined all the data of these cell arrays to 8 vectors which will represent my channels. What is your opinion on that? Would work better?

dpb 2017-6-30

As above, it depends on what you've left out...what do you want/need to do with the data when you've gotten it?

If each of these is an independent event, then it may make sense to keep them segregated by using the cell array for each.

But, as outlined, that can still be so but if you're just analyzing each in sequence, then there's not necessarily any reason to keep them all in memory so might as well just use the 2D array for each then proceed to the next.

Still not enough detail to know...

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Answer 1

Jan 2017-6-30

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/346769-concatenate-integer-to-variable-name#answer_272494

编辑：Jan 2017-6-30

在 MATLAB Online 中打开

Result = cell(230, 8, 3);
for j= 1:230
  for i=1:8
    for lvl = 3:5
      Result{j, i, lvl - 2} = wavedec(Ext{j}(:,i+1), lvl, 'haar');
    end
  end
end

Or if the output of wavedec is a scalar:

Result = zeros(230, 8, 3);
  ...
  Result(j, i, lvl - 2) = wavedec(Ext{j}(:,i+1), lvl, 'haar');
  ...

If you have a really good reason to hide the indices in the names of the variables (and I'm convinced that this is rarely useful):

for j= 1:230
  for i=1:8
    for lvl = 3:5
      Name = sprintf(%s_%s_%d', haar_decomp_ext{j,i}, haar_coeff_num_ext{j,1}, lvl);
      Result.(Name) = wavedec(Ext{j}(:,i+1), lvl, 'haar');
    end
  end
end

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Ioannis Agalliadis 2017-6-30

The first applies to my situation! Thank you!

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Answer 2

Steven Lord 2017-6-30

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/346769-concatenate-integer-to-variable-name#answer_272540

"Every column belongs to a different channel and I have 8 columns of them. The first column is the time. The number of rows is different because the time of the movement that I am investigating varies. That means, that I have a variable number of rows always."

If you're using release R2016b or later, consider creating a timetable to store your channel data, using synchronize to merge each new channel into the timetable that will store all your data. If one channel has data at a time another does not, you can have synchronize fill the second channel's entry for that time with missing (for floating-point data, NaN.)

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Concatenate integer to variable name

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Concatenate integer to variable name

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