Speeding up comparison using strcmp

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Yongmin
Yongmin 2015-1-13
评论： Titus Edelhofer 2015-1-13
Hello! I have a list of approximately 2 million records and I would like to compare the records with a list of devices which generates those records. My code is as follows where "c" is the list of records and "device" is the list for distinct devices:
for ii = 1:length(device)
idx = ( strcmp(c,device(ii,:)) );
lidx = find(idx);
devid{ii} = lidx;
end
The problem is the above code takes too long time (more than an hour). Would you please tell me know how to reduce execution time?
Many thanks!
  2 个评论
David Sanchez
David Sanchez 2015-1-13
What do you mean by "list".
Are c and device sell arrays?
Yongmin
Yongmin 2015-1-13
编辑：Yongmin 2015-1-13
Yes, c is cell array and device is array of character strings.

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采纳的回答

Titus Edelhofer
Titus Edelhofer 2015-1-13
Hi,
I would convert device to a cell array (using cellstr) and then call ismember without the loop, something like
cellDevice = cellstr(device);
[~, devid] = ismember(cellDevice, records);
Titus
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Titus Edelhofer
Titus Edelhofer 2015-1-13
I understand. In this case it might be hard without a loop. I'm not sure, but something like this could work then:
[~,idx] = ismember(records, cellDevice);
devid = cell(numel(cellDevice), 1);
for ii=1:length(devid)
devid{ii} = find(idx==ii);
end
Titus
Yongmin
Yongmin 2015-1-13
Wow, the method you told is much faster. Thank you so much for your help!!

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更多回答（1 个）

David Sanchez
David Sanchez 2015-1-13
If you have getnameidx available in your system, you might transform your device to a cell:
device_cell = celstr(device);
and then look for their position within c:
device_positions = getnameidx(c,device_cell);
which will return the position of your devices within the c cell
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Yongmin
Yongmin 2015-1-13
编辑：Yongmin 2015-1-13
Many thanks for your answer. But I don't have getnameidx in my system. Would you please tell me how to get it?
Titus Edelhofer
Titus Edelhofer 2015-1-13
As I said, it's in the Financial Toolbox, but it won't help for your problem.

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