Removing structure field if

Hello,

I have two structures with a different number of fields. Struct1 has 75 fields and Struct2 has 111 fields. I would like to remove the fields from Struct2 that have a fieldname that is not equal to any of the field names in Struct1 so the two structures have the same number of fields with same field names. Alternatively I'd like to create a new structure that only has the fields from Struct2 that have field names equal to Struct1. I've tried for-if loops using 'isfield' and 'rmfield' and so on but I haven't managed to get anything to work yet. I'd really appreciate any help!

Answer 1

[Walter Roberson]

fn1 = fieldnames(Struct1);
fn2 = fieldnames(Struct2);
tf = ismember(fn2, fn1);
NewStruct = struct();
for K = 1 : length(tf)
  if tf(K); NewStruct.(fn2{K}) = Struct2.(fn2{K}); end
end

I expect that is also a vectorized formulation that uses struct2cell()

Answer 2

[the cyclist]

There might be a more efficient way to do this, but here is one way:

S1 = struct('name1',1,'name2',2);
S2 = struct('name1',1,'name3',3);

F1 = fieldnames(S1);
F2 = fieldnames(S2);

fieldsToRemove = setxor(F1,F2);

fieldsToRemoveFromS1 = intersect(F1,fieldsToRemove);
fieldsToRemoveFromS2 = intersect(F2,fieldsToRemove);

S1 = rmfield(S1,fieldsToRemoveFromS1)
S2 = rmfield(S2,fieldsToRemoveFromS2)

[the cyclist]

Note that this method also removes fields from S1 that are not in S2, so you should get rid of that code if you didn't want that.

Answer 3

[Jan]

Or:

fn1 = fieldnames(Struct1);
NewStruct = struct();
for K = 1 : length(fn1)
  NewStruct.(fn1{K}) = Struct2.(fn1{K});
end

This has the advantage that the fieldnames of Struct1 and NewStruct have the same order, such that they can be joined to a struct array.

[Walter Roberson]

Clear and simple.

The difference between your code and mine is that yours assumes that all fields in Struct1 will appear in Struct2 for sure.

[Jan]

@Walter: To be true, I've filleted your code, because I need some variables called "fn2" and "tf" as well as an intersect() for my own programs. :-)

I assume, my "keep it simple stupid" approach could match Anna's needs.

Answer 4

[Anna]

Thanks so much for your inputs, problem solved :)