Function with a structural array

I am trying to make a function that generates a structural array:

function [ schedule ] = addGameStruct( schedule,hometeam,awayteam,homescore,awayscore )
%ADDGAMESTRUCT 
%   schedule is a structure with fields hometeam, awayteam, homescore,
%   awayscore, and winner that holds the current data and will be expanded
%   to include a new game
%   hometeam: home team's final score
%   awayscore: away team's final score
%
field1='hometeam'; 
field2='awayteam';
field3='homescore';
field4='awayscore';
field5='winner';
value1=hometeam;
value2=awayteam;
value3=homescore;
value4=awayscore;
value5='Cal';
%
s=struct(field1,value1,field2,value2,field3,value3,field4,value4,field5,value5);
schedule={schedule;s};
end

However, the above code produces a 2x1 cell array when I would like to produce a structure array. How do I make a structure array?

Answer 1

[Cedric]

Concatenation is done using square brackets []. Curly brackets are for defining cell arrays. Also, while it is a question of preference, we generally avoid defining variables for storing all field names and values. Instead, we use directly the strings and values in the call to STRUCT.

To illustrate:

 function schedule = addGameStruct(hometeam, awayteam, homescore, awayscore, schedule)
    %ADDGAMESTRUCT 
    %   schedule is a structure with fields hometeam, awayteam, homescore,
    %   awayscore, and winner that holds the current data and will be expanded
    %   to include a new game
    %   hometeam: home team's final score
    %   awayscore: away team's final score

    % - Set default empty array to schedule when not passed (init).
    if nargin < 5
        schedule = [] ;
    end

    % - Build data struct.
    s = struct('hometeam', hometeam, 'awayteam', awayteam, 'homescore', homescore, ...
        'awayscore', awayscore, 'winner', 'Cal') ;

    % - Append data struct (concatenate) to schedule struct array.
    schedule = [schedule; s] ;

 end

Note that I pass schedule as last element and test whether something was passed. This allows to pass nothing when initializing the schedule with a first entry.

 >> schedule = addGameStruct('A', 'B', 10, 5) ;
 >> schedule = addGameStruct('C', 'D', 8, 12, schedule) ;
 ..

but this too is a question of personal preference. Finally, note that using STRUCT2TABLE is useful for displaying struct arrays (e.g. for debugging):

 >> struct2table(schedule)
 ans =
  2×5 table

    hometeam    awayteam    homescore    awayscore    winner
    ________    ________    _________    _________    ______

    'A'         'B'         10            5           'Cal' 
    'C'         'D'          8           12           'Cal'

PS: and if once you want to extend this exercise with object oriented MATLAB, this is one way to do it: define a class Schedule saved in Schedule.m :

    classdef Schedule < handle
        properties
            data
        end
        methods
            function obj = Schedule(varargin)
                obj.data = struct('hometeam', {}, 'awayteam', {}, 'homescore', [], ...
                    'awayscore', [], 'winner', {}) ; 
                if nargin
                    obj.add(varargin{:}) ;
                end
            end
            function add(obj, hometeam, awayteam, homescore, awayscore)
                dId = numel(obj.data) + 1 ;
                obj.data(dId).hometeam  = hometeam ;
                obj.data(dId).awayteam  = awayteam ;
                obj.data(dId).homescore = homescore ;
                obj.data(dId).awayscore = awayscore ;
                obj.data(dId).winner    = 'Cal' ;
            end
            function dispTable( obj )
                disp(struct2table(obj.data)) ;
            end
        end
    end

and then you can create an object and "talk" to it (no need to pass a struct array to a function that returns another struct array, as data and functions are grouped in the class:

 >> schedule = Schedule() ;
 >> schedule.add('A', 'B', 10, 5) ;
 >> schedule.add('C', 'D', 8, 12) ;

or more concisely:

 >> schedule = Schedule('A', 'B', 10, 5) ;
 >> schedule.add('C', 'D', 8, 12) ;

and then

 >> schedule.dispTable
    hometeam    awayteam    homescore    awayscore    winner
    ________    ________    _________    _________    ______

    'A'         'B'         10            5           'Cal' 
    'C'         'D'          8           12           'Cal'