How to access and use specific data from a structure

Question

Artu 2012-6-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/41986-how-to-access-and-use-specific-data-from-a-structure

Hello there!

So have a structure 1x1 with 10 (8760x1) elements. I want to create a script to access to each of these 10 groups of data and I want to evaluate different functions and in order to get a vector with the result of the evaluated function.

For example, I want to access the data to get the maximum value at each time, so I want to get a vector with ten elements showing me the maximum value of each group of data.

So "Graph" is the name of the structure, and "Curve'n' " is each of the 10 arrays that I need to evaluate. I have used this and it works but I find it not very practical because I have to write the whole expression down

    m(i)=max(Graph.Curve1);
     m(i+1)=max(Graph.Curve2);
    m (i+2)=max(Graph.Curve3);
    m (i+3)=max(Graph.Curve4); ...... and so on till 10

I have tried

for i=1:10;
    m(i)=max(Graph.Curve"i");
end
m

But it doesn't work.

Is there a more practical way to do this?

Thank you very much.

Best regards.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Walter Roberson 2012-6-25

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Andrei Bobrov 2012-6-25

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/41986-how-to-access-and-use-specific-data-from-a-structure#answer_51737

在 MATLAB Online 中打开

m = structfun(@max,Graph);

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Artu 2012-6-27

I find this very helpful and practical. Thanks.

请先登录，再进行评论。

Answer 2

Tom 2012-6-25

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/41986-how-to-access-and-use-specific-data-from-a-structure#answer_51729

在 MATLAB Online 中打开

You can avoid using a loop altogether:

m=cellfun(@max,struct2cell(Graph));

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Artu 2012-6-27

This works too. Thank you

请先登录，再进行评论。

Answer 3

grapevine 2012-6-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/41986-how-to-access-and-use-specific-data-from-a-structure#answer_51700

在 MATLAB Online 中打开

Try to use this function : eval Use my code as example

Graph.Curve1=[1 2]
max(eval(['Graph.Curve',num2str(1)]))

good luck

3 个评论
显示 1更早的评论隐藏 1更早的评论

grapevine 2012-6-26

i don't get it

why not?

Using eval hurts someone, doesn't it?

http://www.mathworks.fr/matlabcentral/answers/?search_submit=answers&query=eval+problem&term=eval+problem

Artu 2012-6-27

I am new on this programming thing so I will be careful if EVAL is not a very reliable function. Thanks.

请先登录，再进行评论。

Answer 4

Jan 2012-6-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/41986-how-to-access-and-use-specific-data-from-a-structure#answer_51710

在 MATLAB Online 中打开

Graph.Curve1 = [1 2];
max(Graph.(sprintf('Curve%d', 1)))

This method is called "dynamic fieldnames". In opposite to the evil eval it is safe, fast, easy to debug and let Matlab to process the code efficiently.

It is a good programming practice not to include indices in the names of variables. Obviously indices are a good method to implement indices, e.g.: Graph.Curve{1}, Graph.Curve{2}, ...

2 个评论
显示无隐藏无

Image Analyst 2012-6-25

Artu you can do it this way, but which way do you think is easier for someone else to understand when it comes time for them to take over your code, or when you look at it a year from now, dynamic field names, or the way you did it at first? If you gave Tom's, andrei's, Jan's, and your code to your classmate, which would he understand? Not to say that dynamic field names don't have their place, but come on, it's only 10 lines of code - not that many. If you had hundreds of them then that might be a different matter. Not to take anything away from Jan's clever solution, but personally I'd vote in favor of the way you originally did it as being the way that is easier to understand. For me, I always keep in mind maintainability and not just compactness when writing code. I'm probably in the minority but that's just my 2 cents...

Artu 2012-6-27

You are right. It's always better to use the way we can understand easier. Maybe we worry too much about the compactness thing. I will keep your suggestion on mind. Thanks

请先登录，再进行评论。