Matlab: Appending structure with new field dynamically in loop

Question

I a bunch of data structures with an id (id1, id2, id3, ... idN) a single data field that contains variables (var1,var2,var3, ... varK), such that the first structure looks like

id1.data.variable1 = []
id1.data.variable2 = []
.
.
.

All id's share the same data and variable structure.

Now, I would very much like to append a new variable (newvar) to these existing structures in a loop.

For one structure, I would just do this:

id1.data.newvar1 = id1.data.var1^2

which would add newvar1 to my id1.data with id1.data.var1^2 as values.

If i try

for i = 1:length(id_list)
      id_list{i}.data.newvar = id_list{i}.data.var1^2
end

I get a "Struct contents reference from a non-struct array object." error.

Any input is appreciated.

you are referencing id_list{i} as if it were a cell array. The error is because you try to reference the contents of that cell array as if it were a structure. What exactly is id_list? You might want to try (id_list{i}) if id_list is the list of all field names. — adjpayot

Víctor Martínez Víctor Martínez · Accepted Answer · 2016-09-29T11:33:01

You can create a new global struct that contains the set of structs that you are working with. Thus, the new struct will have the following fields:

ID.id1, ID.id2, ..., ID.idnumber_of_ids

So, in order to loop each id#:

for i = 1:number_of_ids
    name = ['id' num2str(i)];
    ID.(name).data.newvar = ID.(name).data.var1^2;
end

Finally, save the struct without the ID high-level:

save('here.mat','-struct','ID');

Matlab: Appending structure with new field dynamically in loop

1 Answers