Find a match in a structure array using arrayfun
11 views (last 30 days)
Show older comments
Hi there,
I have some data stored in a structure array s, with the following fields: s.Month, s.Day, s.Hour and s.Data. The structure array has the size of 1x123, i.e.a time series of 123 time steps.
I try to find a certain set within the structure array, matching the date, say 08/21 00 UTC.
My idea was:
m = 8; d = 21; h = 0;
index = find( arrayfun(@(x) x.Month==m & x.Day==d & x.Hour==h, s) );
data = s(index).Data;
But the result of arrayfun() is an empty matrix. (I know that the index must be 81.)
What actually works is:
find( arrayfun(@(x) x.Month==m,s) & ...
arrayfun(@(x) x.Day==d,s) & ...
arrayfun(@(x) x.Hour==h,s) )
ans =
81
My question is: why does the first option not work ?
Thank you for an answer.
3 Comments
dpb
on 5 Jun 2014
Edited: dpb
on 5 Jun 2014
If it walks like a duck, quacks like a duck, plays golf like the AFLAC duck, ... :)
OKAY, I always start out thinking I've just got a comment then something happens--like the realization of the [] to build the arrays above was after I was already to sign off having simply noted his solution worked for me. I don't follow what didn't in his case, yet, however...
I'd noticed you'd been pinging a bunch but I'm not sure I'll live long enough to get to the privilege level of any significance... :)
The only thing I miss as structured is that sometimes it would be good to re-edit a submission but it takes excessive amount of time already. What I really miss that doesn't seem to exist at all is for feedback from the privileged be considered in updating the forum. It wouldn't be necessary to have to re-edit so much code if the default weren't wordwrap and a few other details like that...there is so much wasted effort in cleaning up happening even as it is and not a tenth of what should gets done.
Image Analyst
on 5 Jun 2014
You're not far from 2000 when you'll be able to edit posts of others. I'll help by giving you 2 points per vote so you'll be there shortly.
Accepted Answer
dpb
on 5 Jun 2014
Edited: dpb
on 5 Jun 2014
Not certain; it did for a small sample case here...but you can write it w/o arrayfun as
ix=find([s.Month]==m & [s.Day]==d & [s.Hour]==h);
making the arrays from the struct.
ADDENDUM
Or, add a datenum value as another field and make your search on the single variable might be faster searching and certainly less complicated to build the search pattern I think. It's certainly much simpler to do ranges that way.
2 Comments
dpb
on 6 Jun 2014
Figured had to be something of the sort; glad you found it.
Interesting that there's that large a speed difference...I hadn't timed it as just used a very short handmade test vector to verify syntax.
More Answers (0)
See Also
Categories
Find more on Matrix Indexing in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!