Sum cumulative value from all files that is summoned in a loop

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SRRellum
SRRellum 2022-4-20
评论： SRRellum 2022-4-20
I want to add the row length of the variable 'time' in a file (length(dataset.time)) from multiple datasets that are summoned in a loop. My setup is a follows:
datafolder = ' Z:\Projects\data';
file = dir(datafolder);
for i = 3:105
patient = load(strcat(datafolder,'\',file(i).name));
dataset = patient.table
row_length = length(dataset.time)
sum_length = ?
For now, ' row_length' only outputs the number of rows from the last dataset.
How do I add the total number of rows from dataset 3:105?
Hope you can help
  2 个评论
Stephen23
Stephen23 2022-4-20
编辑：Stephen23 2022-4-20
This line:
for i = 3:105
is an anti-pattern, buggy attempt to ignore the dot directories:
https://www.mathworks.com/matlabcentral/answers/345841-unexplained-error-on-dir#answer_271627
https://www.mathworks.com/matlabcentral/answers/21150-function-call#comment_46042
https://www.mathworks.com/matlabcentral/answers/394807-create-text-file-containing-list-of-file-names#comment_556641
https://www.mathworks.com/matlabcentral/answers/288815-gui-for-loop-not-working-correctly#answer_224956
https://www.mathworks.com/matlabcentral/answers/484430-using-struct-dir-selpath-what-do-and-mean-as-struct-name#answer_395754
https://www.mathworks.com/matlabcentral/answers/40949-omitting-pointers-when-listing-folder-contents#answer_50568
https://www.mathworks.com/matlabcentral/answers/13978-list-of-files-sorting#answer_19278
As Walter Roberson wrote in that last link: "In short: if your code assumes that '.' and '..' are the first two entries in a directory, your code has a bug (even in MS Windows). If your code assumes that directory entries are returned in any sorted order, your code has a bug (in all OS.)"
Much better code uses ISMEMBER or SETDIFF.
SRRellum
SRRellum 2022-4-20
Thanks, good point. This was indeed the easy way out. I will change it

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采纳的回答

Davide Masiello
Davide Masiello 2022-4-20
Inside the loop write
row_length(i) = length(dataset.time);
After the loop, you can calculate the summ of all lengths with
sum_length = sum(row_length);
  1 个评论
SRRellum
SRRellum 2022-4-20
Thanks for yout help. It works, however it gives the message to consider preallocating. Will look into that.

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更多回答（1 个）

David Hill
David Hill 2022-4-20
datafolder = ' Z:\Projects\data';
file = dir(datafolder);
row_length = 0;
for i = 3:105
patient = load(strcat(datafolder,'\',file(i).name));
dataset = patient.table
row_length = row_length+length(dataset.time)
end
  1 个评论
Stephen23
Stephen23 2022-4-20
编辑：Stephen23 2022-4-20
Ran in:
Fragile/buggy code:
for i = 3:105
Lets try it with some simple, perfectly valid filenames:
csvwrite('+new.txt',1)
csvwrite('-old.txt',1)
csvwrite('test.txt',1)
dir()
+new.txt -old.txt . .. test.txt
Fragile at best, buggy at worst.

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