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

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?

[Joel Handy]

Do you mean you want to divide your structure array into two smaller arrays or do you want to pull out certain fields from the main structure to form a new smaller structure?

If the former

Structure_1 = Structure_Main([Structure_Main.Field_1] < 20);
Structure_2 = Structure_Main([Structure_Main.Field_1] >= 20);

[SS]

Hi. Thanks for the reply. Actually, it is the latter. I want to pull out certain fields and form a new structure.

[Walter Roberson]

Is the desired result 1 x 50000 struct with two fields, each of which is a scalar struct with 30 fields?

Or is the desired result a scalar struct with two fields, one of which is a 1 x something struct array of 30 fields and the other is 1 x (50000 minus something) struct array of 30 fields?

[SS]

Hi. It is the second one.

Answer 1

[Walter Roberson]

mask = [vel.y] <= 20;
result.vel_sub1 = vel(mask) ;
result.vel_sub2 = vel(~mask) ;

Answer 2

[Joel Handy]

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);