MATLAB Answers

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?

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');
  6 Comments
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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