How to access certain elements in Matlab structure array

Question

I am working on a Matlab project that connects with Thingsboard website. I use webread function to get the response from the server which sends information as JSON. When I send a request to get the users' information, I should get the information in the following format:

  [
{
  "email": "Davis@gmail.com",
  "authority": "CUSTOMER_USER",
  "firstName": "Davis",
  "lastName": "Smith",
  "name": "JOHN@gmail.com"
},

  "email": "DONALDSON@hotmail.com",
  "authority": "CUSTOMER_USER",
  "firstName": "DONALDSON",
  "lastName": "ZAIK",
  "name": "meraj@hotmail.com"
},

]

However, the response that I get in Matlab using webread function is as follows:

4×1 struct array with fields:
email
authority
firstName
lastName
name

and when I access any field like email, it shows the emails of all the users as follows:

response = webread("serverurl");

response.email 


ans =

    'Davis@gmail.com'

ans =

    'DONALDSON@hotmail.com'

What I want to know is how to get a specific user's information by knowing one field only. For example, I want to get the email,lastname and authority of the user Davis by knowing the first name "Davis".

I really appreciate your help in this matter.

Did you read [this page of the documentation](https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-structure-array.html)? — Cris Luengo, Nov 17 '19 at 19:27
https://stackoverflow.com/questions/24964753/string-compare-in-struct-matlab/ — Daniel, Nov 17 '19 at 19:57

Rotem · Accepted Answer · 2019-11-17T20:43:08.090

You can use the following syntax:

filtered_response = response(strcmp({response(:).firstName}, 'Davis'));

response(:).firstName lists all first names.
{response(:).firstName} build a cell array of first names.
Example: {'Davis', 'DONALDSON'}
strcmp({...}, 'Davis') Returns a logical array with value 1 where firstName equals 'Davis' and 0 where not equal.
Example: [0 1 0 0] is returned if only response(2).firstName = 'Davis'.
response(strcmp...) Uses logical indices for returning a new array where index equals 1.
Example: response(logical([0 1 0 0])), returns an array (with length 1) containing the second struct of response.

Sample code:

%Build an array containing two structures (just for the example)
%Assume response is the result of webread 
response = [struct('email', 'Davis@gmail.com', 'authority', 'CUSTOMER_USER', 'firstName', 'Davis', 'lastName', 'Smith', 'name', 'JOHN@gmail.com');...
            struct('email', 'DONALDSON@hotmail.com', 'authority', 'CUSTOMER_USER', 'firstName', 'DONALDSON', 'lastName', 'ZAIK', 'name', 'meraj@hotmail.com')];

filtered_response = response(strcmp({response(:).firstName}, 'Davis'));

Result:

filtered_response = 

  struct with fields:

        email: 'Davis@gmail.com'
    authority: 'CUSTOMER_USER'
    firstName: 'Davis'
     lastName: 'Smith'
         name: 'JOHN@gmail.com'

Now you can get any field like filtered_response.email in case there is only one struct with firstName = 'Davis'.
And filtered_response(:).email in case there is more than one matching struct.

How to access certain elements in Matlab structure array

1 Answers1