OOP: Select Data with conditional

4 次查看（过去 30 天）
Nycholas Maia
Nycholas Maia 2018-11-27
编辑： Matt J 2018-11-29
I would like to filter a array of objects (animal class) and get a new array of objects that fits in 2 properties conditions simultaneally.
Example:
I want to get all animals that have more than 5 years old and less than 10 inches of height.
My animal class is:
classdef animal
properties
age % years
height % inches
name % string
end
end
So I can create animals objects like
dog1 = animal();
dog1.age = 10;
dog1.height = 15;
dog1.name = "Bob";
cat1 = animal();
cat1.age = 2;
cat1.height = 10;
cat1.name = "Alice";
And than put all animals objects in same array, like:
my_array = {dog1, cat1, ...};
How can I "filter" my_array using 2 conditionals (age and height)?

请先登录，再回答此问题。

采纳的回答

Luna
Luna 2018-11-27
Hi Nycholas,
Try this code below. Filtered array will return to you Jessie and Kayle which meets the conditions.
dog1 = animal();
dog1.age = 10;
dog1.height = 15;
dog1.name = 'Bob';
cat1 = animal();
cat1.age = 2;
cat1.height = 10;
cat1.name = 'Alice';
dog2 = animal();
dog2.age = 10;
dog2.height = 8;
dog2.name = 'Jessie';
cat2 = animal();
cat2.age = 6;
cat2.height = 3;
cat2.name = 'Kayle';
my_array = {dog1, cat1,dog2,cat2};
idx = logical(zeros(1,numel(my_array)));
for i = 1:numel(my_array)
if my_array{i}.age > 5 && my_array{i}.height < 10
idx(i) = true;
end
end
filteredArray = my_array(idx);
  4 个评论
显示 2更早的评论
Nycholas Maia
Nycholas Maia 2018-11-28
Sure Luna, you are right!
In the end of the day, I'm thinking to use vectors (or a big matrix) to do these operations above.
I was just trying to implement the same idea using OOP, because, in my opinion, the code stays more "clear"...but, any way...
I put here the "animal class" just to abstract my real problem: Read/Import all musical notes from a digital music score/sheet and use MATLAB to analysis the music score in mathematics way...
So, my read/import process is a "for loop" statement that runs on each note of my music score file. Inside this "for loop" I was creating a "musical note" object from the class below:
classdef musical_note
properties
midi_note % Scalar value, like: 60
duration % in seconds, like: 0.5
bar % or measure, like: 1578
instrument % Instrumen who is playing this note, like: "Piano"
Other1 % Other parameter of the musical note...
Other2
Other3
OtherN
end
end
After the import process, I will have the 'my_array' filled with all music_notes object.
Now, I would like to filter this array, in some "magical way", like:
filtered_array = some_function(my_array, midi_note = 50, duration > 10, instrument = "Piano")
As you well said, I think that the best way to implement this is creanting a big matrix and not use OOP. Right?
Thank you for your quickly answer!
Luna
Luna 2018-11-29
编辑：Luna 2018-11-29
It does nothing to do with OOP, I think what you need is a kind of table structure for that magical way below.
filtered_array = some_function(my_array, midi_note = 50, duration > 10, instrument = "Piano")
You should set a good defined tables for what you need or be using a database.
(You can still continue to use OOP)

请先登录，再进行评论。

更多回答（1 个）

Matt J
Matt J 2018-11-29
编辑：Matt J 2018-11-29
In this scenario, it is better to have a single object whose properties are arrays than an array of objects whose properties are scalars. However, the following should be faster than looping,
my_array = [my_array{:}]; %get rid of cell array storage
conditions = [my_array.age]>5 & [my_array.height]<10;
filtered_array = my_array(conditions);

类别

在 Help Center 和 File Exchange 中查找有关 Construct and Work with Object Arrays 的更多信息

标签

产品


版本

R2018b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by