how to find the index of an object with certain property value in an array?-CodePudding

For example, I create a class 'student'

classdef student

 properties
    name
    sex
    age
 end

 methods
    function obj = student(name,sex,age)
    obj.name = name;
    obj.sex = sex;
    obj.age = age;
 end
end

and then create some objects in an array 'school'

school(1)=student(A,'boy',19)
school(2)=student(B,'girl',18)
school(3)=student(C,'boy',20)
school(4)=student(D,'girl',19)

My question is how to find the index of the objects with certain properties in the array 'school'?

For example, if I want to find students with age 19, the result will be index [1,4]

If I want to find students with age 19 and sex 'boy', the result will be index [1]

Further question 1: how to find the row and colume index? The object with sex 'girl' and age 19 lies in row 1 colume 4.

Further question 2: if school is an cell array, how to solve above problems?

CodePudding user response：

Seems kind of homework questions. However here are the answers:

% find students with age 19,
find (  [school(:).age] == 19 )

% find students with age 19 and sex 'boy', 
find (  [school(:).age] == 19 & strcmp( { school(:).sex }, 'boy'   ) )

% how to find the row and colume index? 
[row, col] = ind2sub( size(school), find (  [school(:).age] == 19 & strcmp( { school(:).sex }, 'girl'   ) ) )

Considering the last question, I would convert the cell of school objects back into an array and do as shown above.

CodePudding user response：

If school is a cell array so you have

school = cell(4,1);
school{1}=student(A,'boy',19)
school{2}=student(B,'girl',18)
school{3}=student(C,'boy',20)
school{4}=student(D,'girl',19)

Then you can loop through them to evaluate your conditions. A concise way to do this is with cellfun:

boolAge19 = cellfun( @(x) x.age == 19, school );
idxAge19  = find( boolAge19 );
boolBoy   = cellfun( @(x) strcmp( x.sex, 'boy' ), school );
idxBoy    = find( boolBoy );
boolBoyAnd19 = boolAge19 & boolBoy;
idxBoyAnd19  = find( boolBoyAnd19 );

You can of course skip intermediate steps, the lines just get dense

idxBoyAnd19 = find( cellfun( @(x) x.age == 19, school ) & ...
                    cellfun( @(x) strcmp( x.sex, 'boy' ), school ) );