For Loop using xlsread indexing

Question

James 2020-7-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/558593-for-loop-using-xlsread-indexing

评论： Walter Roberson 2020-7-2

The following loop is giving me a warning of "The variable 'raw' appears to change size on every loop iteration (within a script). Consider preallocating for speed."

for Str = {'Red' 'Green' 'Orange' 'Purple' 'Pink'};
folder = '';
FileNames=dir('.xls');
for i = length(FileNames)
    FileToLoad = FileNames(i).name;
    [~,~,raw{i}] = xlsread(FileToLoad);
    if exist(FileToLoad , 'file')==0
        continue;
    end
end
return;
end

Also, when the files are read into the 'raw' container they are not in the same order as they are listed in the Str. I want the files to be listed in raw table in the order that they are listed in the Str. Is this possible, as I use those indexes later on in my code.

Any suggestions are appreciated. Thanks

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James 2020-7-2

I take the indexes of the .xls files after I xlsread the files into raw. Then those indexes of the raw I process later on in my code. They maybe in my folder ie( Orange.xls, Pink.xls, Red.xls, Green.xls) But I want them listed in the raw table as they are designated in the Str:

Red.xls

Green.xls

Orange.xls

Purple.xls

Pink.xls

Also, I want to load Red.xls then Green.xls then Orange.xls then Purple.xls and then Pink.xls. If lets say, Orange.xls is not in the folder, then I want to leave that index for Orange.xls empty and move on to find the remaining files.

For Example in the raw table if Orange.xls was missing in folder:

index 1 Red.xls

index 2 Green.xls

index 3

index 4 Purple.xls

index 5 Pink.xls

I use the indexes of the files later on in my code.

dpb 2020-7-2

编辑：dpb 2020-7-2

在 MATLAB Online 中打开

Well, it will stop when it's run a maximum of length(FileNamess) times; it's a counted loop. Of course, that could be a sizable number depending on what FileNames contains.

length is risky depending -- altho if one presumes based on use of the .Name field FileNames is the result of a dir() call (did you use wildcard to eliminate the "., .." directory entries?) it is a 1D struct array so you get what you expect. Read the documentation for length to see why it's not good in general.

The exist test is pretty-much pointless; dir() won't return an entry for a non-existing file so if you use something like

d=dir(fullfile('directoryString'),'*.xlsx');
for i=1:numel(d)
  ..
end

you'll only have the files with .xlsx extension; refine the wildcard expression to be more selective.

As far as the raw, save a variable, but the raw data will be a cell array of the size of the elements in the worksheet; it would probably be better to process each in turn before going on to the next--otherwise, you'll have to do something like create a 3D cell array or a cell array of cell arrays.

You also should probably look at and seriously consider readtable and returning the data as MATLAB table instead of the raw cell data.

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Answer 1

Walter Roberson 2020-7-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/558593-for-loop-using-xlsread-indexing#answer_460247

编辑：Walter Roberson 2020-7-2

在 MATLAB Online 中打开

basenames = {'Red' 'Green' 'Orange' 'Purple' 'Pink'};
nbase = length(basenames);
raw = cell(nbase, 1);
for K = 1 : nbase
    FileToLoad = [basenames{K} '.xls'];
    if exist(FileToLoad, 'file')
      [~,~,raw{K}] = xlsread(FileToLoad);
    end
end