MATLAB: 2×1 structure array to structure array

functionstructure array

I have a code:

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';
 schedule=struct(field1,value1,field2,value2,field3,value3,field4,value4,field5,value5);
schedule=[schedule;struct(field1,value1,field2,value2,field3,value3,field4,value4,field5,value5)];
end

That when running the command:

 calSchedule=addGameStruct(struct,'UNC','Cal',30,35)

returns the answer:

calSchedule = 
2×1 struct array with fields:
  hometeam
  awayteam
  homescore
  awayscore
  winner

However, I want to produce a structure array like the following:

>> calSchedule = addGameStruct (struct , ‘UNC ’ , ‘Cal ’ , 30 , 35)
calSchedule =
struct with fields :
hometeam : ‘UNC ’
awayteam : ‘Cal ’
homescore : 30
awayscore : 35
winner : ‘Cal ’

Why doesn't my current function produce a single structure array?

Best Answer

You explicitly add that 2nd struct element with this line:

schedule=[schedule;struct(field1,value1,field2,value2,field3,value3,field4,value4,field5,value5)];

Did you mean for your code to add another element to a passed in schedule? E.g.,

new_schedule = struct(field1,value1,field2,value2,field3,value3,field4,value4,field5,value5);
schedule = [schedule;new_schedule];

Related Solutions

MATLAB: Function with a structural array

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'

MATLAB: Adding empty numerical fields in structure array

Yes, that's simple:

    A.field4 = [];
    A.field5 = [];

&nbsp

In response to comment

    >> clear A
    >> A.f1=1;
    >> A.f2=2;
    >> A.field5 = [];
    >> A.field4 = [];
    >> A
    A = 
            f1: 1
            f2: 2
        field5: []
        field4: []
    >>

So far so good.

    >> A=[A,A]
    A = 
    1x2 struct array with fields:
        f1
        f2
        field5
        field4
        f3
    >> A.f4 = []
    Incorrect number of right hand side elements in dot name assignment.  
    Missing [] around left hand side is a likely cause.

Ok, I missed that you have a struct array

    >> A(1).f4 = []
    A = 
    1x2 struct array with fields:
        f1
        f2
        field5
        field4
        f3
        f4
    >> A(1).f4 
    ans =
         []
    >> A(2).f4
    ans =
         []

Or better

    >> [A.f5] = deal([])
    A = 
    1x2 struct array with fields:
        f1
        f2
        field5
        field4
        f3
        f4
        f5

Best Answer

Related Solutions

MATLAB: Function with a structural array

MATLAB: Adding empty numerical fields in structure array

Related Question