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I have a matlab data structure that is 1 x 500 for a whole plethora of measures, stored as fields. Each subject has values reported in each field. I need to create a new field that is the subtraction of two fields that already exist. I know that it needs to involve a for loop somehow, but I'm a bit lost how to accomplish this.

Amro
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user3216718
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  • yes you can by creating a field dynamically. http://stackoverflow.com/questions/3753642/how-can-i-dynamically-access-a-field-of-a-field-of-a-structure-in-matlab?rq=1 – Lokesh A. R. Jan 20 '14 at 20:59

1 Answers1

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Here is an example:

% lets create a 1x2 structure array with two fields x and y
clear s
s(1).x = 1;
s(1).y = 10;
s(2).x = 5;
s(2).y = 8;

% compute the subtraction of the values y-x
z = num2cell([s.y] - [s.x]);

% create the new field
[s.z] = deal(z{:});

Here is the resulting structure array:

>> whos s
  Name      Size            Bytes  Class     Attributes

  s         1x2               912  struct   

>> s(1)
ans = 
    x: 1
    y: 10
    z: 9

>> s(2)
ans = 
    x: 5
    y: 8
    z: 3

Alternatively, you could always write a straightforward for-loop:

for i=1:numel(s)
    s(i).w = s(i).y - s(i).x;
end
Amro
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