Matlab: How to load a file as array of structs - matlab

Question

I am trying to convert data file (here string representing file with three lines) into a structure array like this:
cel = textscan('1 1.1 2 2.2 3 3.3', '%u %f');
str = cell2struct(cel, {'f1', 'f2'}, 2);
However, now I have a struct array of dimension 1x1, where I can only access the columns using array's fields, but not the whole rows (like 'str(2)' for the second row).
What I need is to have an array of structs (or how it can be called) like this:
str = struct('f1', {1, 2, 3}, 'f2', {1.1, 2.2, 3.3});
because now I can (for instance) filter it like this:
subStr = str(find([str.f1] > 1))
which I could not do in the first case.
Any idea how to get there?
At the end I was able to do it by:
cel = textscan('1 1.1 2 2.2 3 3.3', '%u %f');
[f1, f2] = cel{:};
str = struct('f1', num2cell(f1'), 'f2', num2cell(f2'));
But it does not feel right and I am afraid it will be expensive (the files are quite large).
EDIT:
My solution is indeed too memory demanding, therefore not usable.
Typical files have header, footer, and c. 5e6 lines of data in six columns.
Thanks

Answer 1

It's easier if you're actually working with a file that contains lines. For example, if data.txt contains:
1 1.1
2 2.2
3 3.3
And now you can simply load this using:
tbl = readtable('data.txt');
tbl.Properties.VariableNames = {'f1', 'f2'};
Which results in much nicer (imho) filtering syntax:
subTbl = tbl(tbl.f1 > 1, :);
I suggest you read a bit about tables in MATLAB, to learn about their (many) capabilities.
Finally, if you insist on working with struct arrays, you can do:
str = table2struct(tbl); 3×1 struct array with fields: f1 f2

Answer 2

Each element of cel is an array. Using cellfun and num2cell they can be converted to cell arrays:
names = {'f1', 'f2'};
cel = textscan('1 1.1 2 2.2 3 3.3', '%u %f');
cel2 = cellfun(#num2cell, cel, 'UniformOutput', 0);
prep = [names;cel2];
str = struct(prep{:}).';

Answer 3

I wish I would read those more carefully sooner, but according to this and this it is not encouraged to save large datasets the way I was trying to, because
Structures with many fields and small contents have a large overhead and should be avoided. A large array of structures with numeric scalar fields requires much more memory than a structure with fields containing large numeric arrays.
and
For structures and cell arrays, MATLAB creates a header not only for each array, but also for each field of the structure and for each cell of a cell array. Because of this, the amount of memory required to store a structure or cell array depends not only on how much data it holds, but also on how it is constructed.
So therefore array str.f(1:N) requires (for larger N) much more memory than str(1:N).f.