how to get the specific member data from a struct array?

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xiao 2016-11-4

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评论： Alexandra Harkai 2016-11-7

for example,

b=struct('name','JPEG','age','18') ;
c=repmat(b,3,1) ;
d=c.name;
c.name

why is the result of "c.name" different from the result of "d=c.name"?

how to get the member data directly from a struct array or matrix? such as c.name?

and another question, how to create a struct array or matrix directly just like zeros(2,3), but struct(2,3) doesn't work, so how?

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Answer 1

George 2016-11-4

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在 MATLAB Online 中打开

From the doc on struct

"When you access a field of a nonscalar structure, such as s.f, MATLAB® returns a comma-separated list. In this case, s.f is equivalent to s(1).f, s(2).f, s(3).f."

So your d = c.name is equivalent to

d = c(1).name, c(2).name, c(3).name.

Try

[d,e,f] = c.name

to see the difference. See here for more info on how to access data in a struct.

struct(2,3) doesn't work because it's trying to create a 1x1 struct array with field:2 and value:3. Field needs to be a char array.

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xiao 2016-11-5

thank you! inspired by you, i try d = [c(1).name, c(2).name, c(3).name] and

d=[c.name] for a large struct to put the result together, but need to redivide

the result array. so maybe for loop is required.

and to create a struct matrix, maybe the for loop method or repmat way is needed.

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Answer 2

Alexandra Harkai 2016-11-4

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编辑：Alexandra Harkai 2016-11-4

What c is is what is called a nonscalar struct array. Then "You cannot assign the list to a single variable with the syntax v = s.f because the fields can contain different types of data." as per the Documentation, so variable d gets only c(1).name, and hence they will be different.