How to assign multiple structures in a struct array in Matlab

Question

So far I have this,

Order = struct('Name',{},'Item',{},'Quantity',{},'DueDate',{});
Order(1).Name = 'Order 1'; Order(1).Item = 'Rolo'; Order(1).Quantity = '1'; Order(1).DueDate = '735879';
Order(1).Name = 'Order 1'; Order(1).Item = 'Trident'; Order(1).Quantity = '2'; Order(1).DueDate = '735887';
Order(2).Name = 'Order 2'; Order(2).Item = 'Hershey';Order(2).Quantity = '3'; Order(2).DueDate = '735875';
Order(3).Name = 'Order 3'; Order(3).Item = 'Kitkat'; Order(3).Quantity = '6'; Order(3).DueDate = '735890';

Within each order, there are multiple items and quantities of items, so I would like each struct array for each order to be able to hold multiple items, quantities, and due dates of orders.

Thank you!

Which Matlab version are you using?

Oleg
– Oleg

2014-09-29 14:55:51 +00:00
Commented Sep 29, 2014 at 14:55 — Oleg
– Oleg, Commented Sep 29, 2014 at 14:55

Oleg · Accepted Answer · 2014-09-29 15:49:36Z

The best option is to use table() (or dataset() if your Matlab version is older than 2014a but you have the Statistics toolbox):

Order = table({'Order 1';'Order 2';'Order 3'},...
              {'Trident';'Hershey';'Kitkat'},...
              [2; 3; 6],...
              [735887; 735875; 735890],...
              'VariableNames',{'Name','Item','Quantity','DueDate'})

Order = 
      Name         Item       Quantity    DueDate
    _________    _________    ________    _______
    'Order 1'    'Trident'    2           735887 
    'Order 2'    'Hershey'    3           735875 
    'Order 3'    'Kitkat'     6           735890

You can access it as you would do with a structure but you have more advantages, e.g. accessing and inspecting data is easier, smaller memory footprint etc..

What you are trying to build 'manually' is a structure array (and let me stress the array here):

% A structure array
s = struct('Name',     {'Order 1';'Order 2';'Order 3'},...
           'Item',     {'Trident';'Hershey';'Kitkat'},...
           'Quantity', {2; 3; 6},...
           'DueDate',  {735887; 735875; 735890});

s = 
3x1 struct array with fields:
    Name
    Item
    Quantity
    DueDate

Each scalar structure (/unit/record/object/member call it how you like) of the array will have a set of properties:

s(1)
ans = 
        Name: 'Order 1'
        Item: 'Trident'
    Quantity: 2
     DueDate: 735887

The organization of the data looks intuitive. However, if you want to apply operations across the whole array, e.g. select those which have Quantity > 2, you need to first concatenate the whole field into a temporary array and only then apply your operation, and in the worst case scenario (if you nest the fields) you will have to loop.

I do personally prefer a database/dataset/table approach where each record is a row and columns are the properties. You can do this by flattening the structure array into a scalar structure (pay attention to the braces):

% A flat structure
s = struct('Name',     {{'Order 1';'Order 2';'Order 3'}},...
           'Item',     {{'Trident';'Hershey';'Kitkat'}},...
           'Quantity', [2; 3; 6],...
           'DueDate',  [735887; 735875; 735890]);
s = 
        Name: {3x1 cell}
        Item: {3x1 cell}
    Quantity: [3x1 double]
     DueDate: [3x1 double]

Even though the data organization does't appear as intuitive as previously, you will be able to index directly into the structure (and will have lower memory footprint).

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