How to find indices of elements but keep the order unchanged?

Question

Maria 2014-9-6

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https://ww2.mathworks.cn/matlabcentral/answers/153671-how-to-find-indices-of-elements-but-keep-the-order-unchanged

评论： ibrahim Salim 2018-2-8

Hi all,

I have a cell array ch_names of channel names and I would like to get indexes of certain channels that I have given in pickCh. I have done this as follows:

Idx = find(ismember(ch_names,pickCh));

However, this gives the indexes in increasing order. Is there any better way than using a loop to keep the order of the indexes as it is in pickCh?

Thank you already in advance!

Regards, Maria

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Answer 1

Roger Stafford 2014-9-6

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https://ww2.mathworks.cn/matlabcentral/answers/153671-how-to-find-indices-of-elements-but-keep-the-order-unchanged#answer_150901

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   [tf,loc] = ismember(ch_names,pickCh);
   [~,p] = sort(loc(tf));
   idx = find(tf);
   idx = idx(p);

(This assumes this are no repetitions in 'pickCh'. Otherwise there is ambiguity as to the proper ordering.)

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ibrahim Salim 2018-2-8

Hello, I used this code but I'v changed the first line with : [tf,loc] = cellfun(@(subc) ismember(pickCh, subc,'rows'), ch_names); to seek about a specific row. This line was slow. could you please help me to speed up run time by using the same command or another one.

Thanks

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