Simple wild card function for ismember??

Question

bugguts99 2011-7-19

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https://ww2.mathworks.cn/matlabcentral/answers/11874-simple-wild-card-function-for-ismember

I have a list of dates and times as string values and (e.g '29/1/2010 20:30:00' etc) and I would like to find all values at a specific time, regardless of day.

Is there a simple wild card function that I can use with ismember to identify these? I have tried:

idx = ismember(Timestamp_str, {'*20:30:00'});

I have also tried regexp, searched the web and help files to no avail.....

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Answer 1

Walter Roberson 2011-7-19

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No, there is no wildcard with ismember.

If your Timestamp_str is an array of characters all the same length, then

strcmp(cellstr(Timestamp_str(:,end-7:end)),'20:30:00')

If your Timestamp_str is a cell array of characters, then

cellfun(@(S) strcmp(S(end-7:end),'20:30:00'), Timestamp_str)

Alternately with regexp,

~cellfun(@isempty,regexp(Timestamp_str, '20:30:00$'))

If you just want the true/false of whether there was a match or not. The regexp itself will return the index of the trailing 23:30:00 in each string, with an empty cell for cell entries that do not match.

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Answer 2

Andrei Bobrov 2011-7-19

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d1 = datenum(Timestamp_str);
d2 = datenum('00/0/0000 20:30:00');
out = Timestamp_str(abs(rem(d1,1)-d2)<1e6*eps,:)

ADD variant with 'datevec'

dv = datevec(Timestamp_str);
out = Timestamp_str(all(bsxfun(@eq,dv(:,4:6),[20 30 0]),2),:);

adding in answer on the comment Walter's about milliseconds

dv(:,end) = round(dv(:,end));
dv = datevec(datenum(dv));

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Andrei Bobrov 2011-7-19

Dear Walter! I completely agree with you and thinking about using 'datevec'.

Add variant with 'datevec'

Walter Roberson 2011-7-19

Though 20:29:59.5 and up to but excluding 20:30:00.5 would probably print out as 20:30:00, so rounding the seconds + milliseconds combination might be called for.

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