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Is there a way to perform queries on object collections?

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tombola
tombola 2011-12-16
Hi, I know I can use arrayfun to call a method on each object in an array, but is there a way to perform queries across the array?
This is a made up example, but if I have a class
MATLAB code
classdef Employee
properties
salary = 0; %Set later
end
And I have an array of instances of this class
MATLAB code
staff = [employee1 employee2 employee3 ..... employeeN];
Is there an easy way I can write a query to get, say, the 3 Employees with the largest salarys?
Thanks for any help, just give me a shout if this isn't clear.
Tom.

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采纳的回答

Darik
Darik 2011-12-16
Use comma separated list syntax
staff = [employee1 employee2 employee3 ..... employeeN];
salary = [staff.salary];
[~, i] = sort(salary, 2, 'descend');
top3 = staff(i(1:3))
Keep in mind that if you ever want to subclass your Employee class (into e.g. Secretary and Manager classes) you won't be able to store them all in the same array without converting them all into simple Employee objects.
  2 个评论
tombola
tombola 2011-12-19
That's brilliant, thanks a lot.
Is there any way to remove NaNs from the list please? So if salary is NaN then it doesn't get included in a "top3" or "bottom3" sort?
tombola
tombola 2011-12-19
Hi, I've worked it out.
nanPositions=[isnan(salary)]
staff(nanPositions)=[]
salary(nanPositions)=[]
Then sort. Thanks a lot for the answer above.

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更多回答（1 个）

Sean de Wolski
Sean de Wolski 2011-12-16
Instead of having each employee be its own variable ( like this ) have an employer class with employees as properties and salaries as properties.
There are many example available from the documentation for classdef.

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