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Non Scalar Structures

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Pankaj
Pankaj on 16 Feb 2012
Answered: upol on 10 Jan 2019
Hi how can I save a non scalar structures. Again, I don't really know what a nonscalar structure is. I know mine is a nonscalar structure because save('filename',-struct,'structname) throws exception saying your structure is nonscalar.
I am trying to save a matrix of structures each structure has a structure inside it. does such programming increase runtime?

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Answers (2)

Jan
Jan on 16 Feb 2012
No, such programming does not necessarily increase the runtime. It can be a nice and efficient structure to represent the data. Even if it runs some seconds slower, a clear data representation can save weeks of debugging.
A non-scalar struct is something like this:
S(1,1).a = 1;
S(2,1).a = 2;
S(1,2).a = 3;
S(2,2).a = 4;
Now you have a [2x2] struct with the field 'a'. You cannot save this using the '-struct' flag, but by:
save('filename.mat', 'S');

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Walter Roberson
Walter Roberson on 16 Feb 2012
When you use the -struct flag of save(), the structure itself must be of length 1, only S(1) defined and not S(2) or so on.
The -struct flag is a useful construct to "undo" the effect of loading a .mat file in to a single structure by way of
S = load('YourFile.mat');
The resulting S would be a scalar structure.
If you are not trying to do the opposite of load() in to an output variable then you should probably not be using the -struct flag of save(); it is not needed to save general structures.
Pankaj
Pankaj on 19 Feb 2012
Hi Jan, sorry for late reply.
The code you posted works. I was doing a mistake passing S without single quotes. The issue however is, that this still doesn't solve the problem. It takes Matlab more than half an hour to save the variable.The size of the structure in Bytes is close 5.75 GB.
Any suggestions? thanks
Jan
Jan on 19 Feb 2012
Writing 5.75 GB to a disk takes some time. Do you write the MAT file in the -7.3 format (see "help save", if this is not clear)? You cannot use the faster -v6 flag for SAVE, because even the compressed file is larger than 2GB already.
If your staruct has a lot of elements (millions), consider that each element has more than 100 Bytes overhead. E.g.:
[S(1:1e4).a] = deal(1); T.a(1:1e4) = 1; whos
You have 1200064 Bytes for S and 80176 bytes for T. A struct of fields consumes less memory than a field of structs. This matters the requirements of RAM, of disk-space when using SAVE and even the processing speed depends on the internal data representation.

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upol
upol on 10 Jan 2019
Why this gives problem in C Coder. Error: Directly accessing field or property of nonscalar struct or object not supported for code generation.
s1=string({OPS_FLT(:).ACFT_ID})
s2=OPS_FLT(2).ACFT_ID
uuindex=find(strcmpi(s1,s2))
({OPS_FLT(:).ACFT_ID}) has already been defined as
OPS_FLT(1).ACFT_ID="apple"
OPS_FLT(2).ACFT_ID="orange"
I am trying to find orange from the array. It works in Matlab but not in C Coder

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