How to find number of arrays in a structure filed ?

Question

Raviteja 2011-2-4

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/841-how-to-find-number-of-arrays-in-a-structure-filed

采纳的回答： Siddharth Shankar

在 MATLAB Online 中打开

Hello all,

Av(1).f1=[1 2 3 4]; Av(2).f1=[3 4 5 6]; Av(3).f1=[5 3 2 1]; Av(4).f1=[7 8 2 4];

Av(1).f2=[1 2 3 4 5]; Av(2).f2=[7 6 5 4 3];

I created a structure Av with two fields f1,f2.

I need to konw N1=number of arrays in Av.f1... N2=number of arrays in Av.f2...

So I tried

>> N=size(Av)

N =

     1     4
>> N1=size(Av.f1)
??? Error using ==> size
Too many input arguments.

>> N2=size(Av.f2) ??? Error using ==> size Too many input arguments.

I have to get N1=4, N2=2

Please tell me how to calculate (N1 and N2) ?

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Answer 1

Siddharth Shankar 2011-2-4

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https://ww2.mathworks.cn/matlabcentral/answers/841-how-to-find-number-of-arrays-in-a-structure-filed#answer_1214

在 MATLAB Online 中打开

Off the top of my head:

function [N1, N2] = fieldCount(inputStruct)
N1 = 0;
N2 = 0;
for i = 1: numel(inputStruct)
  if(~isempty(getfield(inputStruct(i),'f1')))
      N1 = N1 + 1;
  end
  if(~isempty(getfield(inputStruct(i),'f2'))) 
      N2 = N2 + 1;
  end
end

You can call this function as follows:

[N1, N2] = fieldCount(Av);

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Answer 2

Fangjun Jiang 2011-2-4

3
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https://ww2.mathworks.cn/matlabcentral/answers/841-how-to-find-number-of-arrays-in-a-structure-filed#answer_1216

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>> sum(~cellfun(@isempty,{Av.f1}))

ans =

4

>> sum(~cellfun(@isempty,{Av.f2}))

ans =

2

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Jan 2011-2-4

With Matt's addition this method is the most efficient solution.

Please, Jiang, insert Matt's addition.

Fangjun Jiang 2011-2-7

Thanks for the tip! cellfun('isempty',...) is much faster than cellfun(@isempty,...) on a large cell array. Where should I get this info? Is it documented? According to the help of cellfun(), function handle is the recommended syntax. The use of strings for a few of those functions is accepted for backward compatibility.

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Answer 3

Sandy Patel 2011-2-4

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https://ww2.mathworks.cn/matlabcentral/answers/841-how-to-find-number-of-arrays-in-a-structure-filed#answer_1223

在 MATLAB Online 中打开

This might be a little confusion on the matlab's data structure.

You could have just as easily made an structure with the following data:

Av(1).f1=[1 2 3 4]; Av(2).f1=[3 4 5 6]; Av(3).f1=[5 3 2 1]; Av(4).f1=[7 8 2 4 999];

Notice the last value made Av(4).f1 one element larger.

In this case

>> size(Av(1).f1,2)
ans =
       4
>> size(Av(4).f1,2)
ans =
       5

So it asking for the size of Av.f1 would not give a unique answer. If you know ahead of time that the size of all the f1 vectors will be the same, then you can just do

size(Av(1).f1,2)

size(Av(1).f2,2)

to get the sizes that you need.

Hope this helps.

Cheers, Sandy