Pre allocating all fields in a structure?

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HRmatlab 2016-8-26

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https://ww2.mathworks.cn/matlabcentral/answers/301003-pre-allocating-all-fields-in-a-structure

评论： James Tursa 2016-8-26

I have several structures that can have variable sizes and must handle a large amount of data of various types. Each structure may have 25 or more fields. I want to preallocate these structures but all the solutions I found preallocate each structure field individually. pseudo code example:

mystructure.a =  preallocate; % using your favorite method
mystructure.b =  preallocate;
....
etc.

Since I have so many fields and multiple structures this becomes rather cumbersome. Is there a way to preallocate all the fields in the structure in one line? Example:

mystructure.all the fields = preallocate; % using your favorite method

Thank you in advance

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Stephen23 2016-8-26

编辑：Stephen23 2016-8-26

According to Loren's blog post, although it is recommended to preallocate the structure itself, preallocating the contents of each field has no effect on the memory used by the structure.

Essentially the structure is one array (which should be preallocated), but each field is its own array quite independent of the structure itself.

James Tursa 2016-8-26

Expanding a bit on Stephen's comment. Preallocating the structure size and field names makes sense, but preallocating (i.e., assigning values to) the field elements themselves usually only makes sense in two special cases:

1) You want to give a large number of field elements a default value, and you only plan on replacing some of the field elements later on with something different.

2) You plan on altering those field elements essentially "in-place" later on as opposed to replacing them with another variable. E.g., if you are just going to replace them with a different variable later on then the preallocation didn't do anything for you other than slow down your code and use memory unnecessarily.

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