Extracting data fom nested object arrays

Question

Sigurd Askeland 2018-4-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/396972-extracting-data-fom-nested-object-arrays

编辑： Matt J 2018-4-24

I have object arrays where the objects have properties that them-self are object arrays. What is the best way to extract data from the "bottom layer"?

A single data point can be accessed in this way:

dataIwant(3,2) = topLayer(3).middleLayerProperty(2).bottomLayerProperty;

Is there a one-liner for creating the entire dataIwant?
Why is this so slow?

    dataIwant = [topLayer.middleLayerProperty];
    dataIwant = [dataIwant.bottomLayerProperty];

It took more than 0.015s for a 600 (top layer) x 4 (middle layer) object array.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Matt J 2018-4-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/396972-extracting-data-fom-nested-object-arrays#answer_316856

在 MATLAB Online 中打开

Is there a one-liner for creating the entire dataIwant?

Not using out-of-the-box MATLAB features, but you can overload the subsref method of the class to have any behavior that you want.

Why is this so slow?

It depends on many factors, such as the memory consumed by the array, your MATLAB version, whether you executed this from the command line or inside a function, whether you ran this once or many times (so that the commands could cache).

But the statements you've shown are not trivial operations. They build whole new arrays, and so require memory allocation and copying. You should consider whether splitting your middle layer across many objects is really the best data organization for you. It might be better to have a single object with an array of middle-layer objects, so that you can index like this

dataIwant(3,2) = topLayer.middleLayerProperty(3,2).bottomLayerProperty;

2 个评论
显示无隐藏无

Sigurd Askeland 2018-4-24

在 MATLAB Online 中打开

Thanks!

Why is this so slow?

I improved the speed three-fold by making the objects inherit handle. (That may come back to bite me...) That would indicate that memory allocation and copying was the problem. It is still as slow as a for loop, though.

Is there a one-liner ...

I would love for there to be at least this kind of functionality:

    dataIwant(:,2) = [topLayer.middleLayerProperty(2).bottomLayerProperty];

Can that be done by overloading the subsref method?

Matt J 2018-4-24

编辑：Matt J 2018-4-24

在 MATLAB Online 中打开

The indexing syntax is totally in your control when you overload subsref. Be mindful, though, that once you do, you will also have to supply definitions of dot-indexing statements, e.g.,