# How to divide a structure into sub-structures based on a condition

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SS on 24 Jul 2019
Answered: Joel Handy on 25 Jul 2019
Hello.
I am new to MATLAB and expecting some help. I have a structure array (1 x 50,000) with 30 fields. I want to divide this structure into multiple structures based on a condition.
I tried sometheing like this. Let the main structure be vel and it has 30 fields. Based on the values of the parameters in the field y of the structure vel, I want to create sub-structures.
for i=1:length(vel)
if y<=20
vel_sub1(i)=vel(i) % creating a new structure
else
vel_sub(i)=[] % null
end
if y>=20 && y<=100
vel_sub2(i)=vel(i) % creating another sub-structure
else
vel_sub(2)=[] % null
end
end
But, unfortunatley I am getting some empty fields in the sub-structure, is there any smart way to implement this without any empty rows in the fields?
SS on 25 Jul 2019
Hi. It is the second one.

Walter Roberson on 25 Jul 2019
mask = [vel.y] <= 20;
result.vel_sub1 = vel(mask) ;
result.vel_sub2 = vel(~mask) ;

### More Answers (1)

Joel Handy on 25 Jul 2019
I think this is what you are looking for. You will end up with two struture arrays both smaller than the original structure array in the number of elements and the number of fields.
sub1Fields = {'Field1', 'Field3', 'Field5'};
sub2Fields = {'Field2', 'Field4', 'Field6'};
vel_sub1 = vel([vel,y] < 20);
vel_sub1 = rmfield(vel_sub1,sub2Fields);
vel_sub2 = vel([vel,y] >= 20);
vel_sub2 = rmfield(vel_sub1,sub1Fields);