You've got a lot in here. I'm going to step through certain parts.
Let's start off with this comment (formatting added, your words are generally in italics):
Set up how I want the table (not that MATLAB will pay any attention)
app.StimInputTable.Data = table('Size',[4 3],...
'VariableTypes',{'categorical','uint8','uint8'});
It did "pay attention" to what you told it to do. Those class calls you made show that. Now the next thing you did:
Read in the file
app.StimInputTable.Data = readtable(infile);
MATLAB changes all the types
Not exactly, though the effect that it had did make the types of the variables in app.StimInputTable.Data different. It didn't change the types; it replaced the entire array that you had in that field of that property, exactly as if you'd typed:
If you ran that example, the complex single scalar value that the first command had assigned to x would be thrown away and the real double vector value that the second command assigned to the name x would take its place. What you wrote is exactly this same idea, just with calls to table and readtable instead of single(1i) and 1:10.
I can redo the .. table(... VariableTypes), but then it tosses all my category data instead of converting
I recommend using detectImportOptions on the file, modifying it if the options that MATLAB detected when it inspected the file don't match what you want, and passing those options into readtable as shown in the "Read Subset of Text File Using Import Options" example on that documentation page. So here's my table, I can deal with the cells
K>> app.StimInputTable.Data
So the char is considered a cell
No. Var1 in this case is a cell array, each cell of which contains a char array. Think of a cell array like a dresser drawer; each drawer can hold socks, or shirts, or underwear, etc. but the drawers aren't themselves socks, shirts, or underwear.
The metaphor breaks down a little since a cell in a cell array can itself contain a cell arrray, the cells of which can contain other stuff.
ok I've seen a warning about how chars (or char vectors) get put into cells, but my users are not going to type "R" 5 0 etc these files already exist.
K>> app.StimInputTable.Data(jj,1)
Try to pull it out and I get another table, not the cell
That's correct. Indexing into a table like that using parentheses gets you another table. This is row 6 in the table summarizing table accessing expressions in the last section on this documentation page. OK so I pull it this way
K>> app.StimInputTable.Data{jj,1}
Correct, indexing into a table with curly braces extracts the contents of the table variable(s). That's row 3 in that summary table.
Now I have a more simple 1x1 cell array, now to the character out of the cell or compare cell to cell
How about I compare it to a cell with the char in it
That looks good, same types, lets try it
K>> app.StimInputTable.Data{jj,1} == {'L'}
Operator '==' is not supported for operands of type 'cell'.
No, that's not going to work. A cell array is a container for data and so not something you're usually going to want to compare with data.
So that didn't work, so I'll try
K>> cl = app.StimInputTable.Data{jj,1}
Get the char out of the cell
Finally!
I'd recommend, unless you have a need to operate with cell arrays of char vectors, that you convert the first variable of your data to a string array and use string comparisons. The == operator is defined for strings, and you can compare string arrays and char arrays using == just fine.
app.StimInputTable.Data.Var1 = string(app.StimInputTable.Data.Var1)
Alternately, if you need to use cell arrays containing char arrays, don't use == for comparison. Use something like matches or the other string manipulation functions instead. Looking at your code:
cl = app.StimInputTable.Data{jj,1}
Is this really what I have to do?
No, and in fact this is not going to work in certain (not uncommon) circumstances. As you've written your code, if cl{1, 1} is the 2-element char array 'LL' MATLAB will enter your if statement body. In addition, if the two char arrays you're comparing have different number of characters, and neither is scalar, like 'Hello'=='Goodbye', MATLAB will error just as though you'd asked it if (1:4) == (1:5).
It took way too long to figure out. I never could find Help on how to extract the single cell of data out of a table. I have R and L as catagories when I use them later but can't read them in as such initing the table size and variabletypes gets ignored by the read()
I recommend using detectImportOptions with readtable to make sure MATLAB imports the data the way you want it, using string arrays if possible, and if you do need to work with char arrays or cell arrays containing char arrays use the string comparison functions listed on this documentation page. Hopefully that page I linked to showing the summary of different ways to access data in tables will be useful to you as well. And if figuring out how to set up the import options programmatically is too time consuming, use the Import Tool to set up your data file how you want it, then generate code by clicking the little down pointing triangle on the Import Selection green checkmark icon and copy and paste that code into your app. Wait a moment
app.StimInputTable.Data{j,1} % This gives a cell as above, but
app.StimInputTable.Data.Var1{j} % is going to work? Where is that documented?
That summary table on the documentation page I linked above that shows the various ways to access data in a table. This is kind of a variant on row 2 in that table, and partly just chaining of dot indexing (to get a cell array) and curly brace indexing into that cell array. It's effectively the same as this operation on a struct whose field contains a cell.
ans =
'L'
So now
if app.StimInputTable.Data.Var1{j} == 'L'
Apparently using .Var1{i} is not the same as indexing with {j}
This works but where will you find it documented? Good luck
See that page with the summary table. It goes into detail about how to work with data in tables.
