One simple solution is to use getfield and setfield to access nested structures. Instead of returning the structure location as one character vector like this:
S = 'data.xlsx.file1.tab1'
you should return it in a cell array of char vectors, like this:
C = {'xlsx','file1','tab1'}
(this will require only a simple change to the recursive function). Then you can trivially access the data using getfield:
getfield(data,C{:})
and that is all! Here is a simple working demonstration:
>> data.xlsx.file1.tab = 1;
>> data.xlsx.file2.tab = 2;
>> data.csv.file2 = 3;
>> C = {'xlsx','file2','tab'};
>> getfield(data,C{:})
ans = 2
No ugly loops, no evil eval, no problems!
"But then again, maybe my whole approach for using such a multi-layered struct is already poor to begin with..."
Personally I am not a big fan of nested structures, and I notice that they tend to be overused by beginners wanting to reflect the minutae of how they see their data-organization. One of the main risks (which you are doing) is encoding meta-data like filenames and tab names into the code (as filednames). This is a bad way to write code: it make code complex and makes accessing that meta-data slow and buggy. Your approach is very fragile, e.g. because there are many filenames that are not valid fieldnames: what would your code do with the filename a-1.csv ? Or a.2.csv? The approach of mixing meta-data (like filenames and tab names) into data is simply flawed, and should be avoided. Meta-data is data, and it should be stored as data in it own right. Consider those example filenames: if we put them into a structure field named filename, then the code will never break depending on the name itself:
S.filename = 'a-1.2.3-4.csv'
You should consider that a table is a very powerful option and has many advantages for processing groups of data.
Personally I would probably use a single non-scalar structure, where the meta-data are simply encoded as data in fields:
data(1).type = 'xlsx'
data(1).name = 'file1'
data(1).tab = 'tab1'
data(1).data = ...
data(2).type = 'csv'
data(2).name = 'file2'
data(2).tab = [];
data(2).data = ...
This would make accessing and processing the data quite simple, and has some neat syntaxes that you will find very handy:
