Speeding up comparison using strcmp

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!

[David Sanchez]

What do you mean by "list".

Are c and device sell arrays?

[Yongmin]

Yes, c is cell array and device is array of character strings.

Answer 1

[Titus Edelhofer]

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

[Yongmin]

Many thanks for your answer. The number of distinct device is approximately 110k and the records for each device can be multiple not just one. So I need to find all the records that contain each device. Would you please help me to refine the code?

[Titus Edelhofer]

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]

Wow, the method you told is much faster. Thank you so much for your help!!

Answer 2

[David Sanchez]

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

[Titus Edelhofer]

Hi David,

this function is from Financial Toolbox. And although it generally speaking is doing what Yongmin wants, it does not handle the multiple occurrences (from the help: NOTE: It will not find multiple occurrences of a name ...). Titus

[Yongmin]

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]

As I said, it's in the Financial Toolbox, but it won't help for your problem.