using a nested for loop to edit a structure

I am trying to edit the tempFactor field in a PDBStruct. I want to use row 1 of matrix4 to search the AtomSerNo field and when they are equal replace the corresponding tempFactor with row 2 of matrix4. This is the code I tried

for i3=1:length(matrix3)
    for i4=1:length(matrix4)
        if PDBStruct.Model.Atom.AtomSerNo(i3)==matrix4(1,i4)
            PDBStruct.Model.Atom.tempFactor=matrix4(2,i4);
        end
    end
end

This is the error I got "Expected one output from a curly brace or dot indexing expression, but there were 30471 results"

I think I just dont understand how to properly search within the structure. This format worked great when I was editing a matrix rather than a structure earlier in my code (example below)

for i1=1:size(matrix1(:,1))
    for i2=1:size(matrix2(:,1))
         if matrix1(i1,1)==matrix2(i2,1)
             matrix1(i1,3)=matrix2(i2,2);
         end
    end
end

[Elissa Moller]

this works but it runs for a really long time

for i3=1:length(matrix3)
    for i4=1:length(matrix4)
        if PDBStructmodel.Model.Atom(i3).AtomSerNo==matrix4(1,i4)
            PDBStructmodel.Model.Atom(i3).tempFactor=matrix4(2,i4);
        end
    end
end

Any suggestions?

[Stephen23]

As an alternative to nested loops you could use both outputs of ismember:

https://www.mathworks.com/help/matlab/ref/ismember.html

for which you will also need to concatenate those values into vectors:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

Answer 1

[Arthur Goldsipe]

As mentioned in the comments, if you want to compare one atom at a time, the proper way to index is Atom(i3).AtomSerNo. But if you want to do the comparison more efficiently, you can "vectorize" the operation to work across all atoms at once using ismember. The way that I would assign values from matrix4 at once requires me to put them all in a temproary cell array. I would write that code something like this:

[serNoIsInMat4, locationInMat4] = ismember([PDBStructmodel.Model.Atom.AtomSerNo], matrix4(1,:));
tempFactorCell = num2cell(matrix4(2,locationInMat4(serNoIsInMat4)));
[PDBStructmodel.Model.Atom(serNoIsInMat4).tempFactor] = tempFactorCell{:};

There might be some mistakes in my code. Since I don't have access to your data, it's hard for me to confirm I wrote things properly. But hopefully this is enough to help you understand how to proceed.