MATLAB: How to extract data from .mat file that contains table

cell arraysMATLABmatrixtable

Hi everyone,

I would like extract data from table on the .mat file. I tried to convert the 'struct' into 'cell' obtaining a cell array 1×1 and then I tried to convert 'cell' into numeric array but cell2mat doesn't support cell array. The goal is to obtaine a matrix of dimension 30932×5. Are there someone that can help me? Thanks.

fileName = 'D:\Valerio\data\data_models\ACCESS1_0.mat';
loadfile = load(fileName);
table = struct2cell(loadfile);
data_matrix = cell2mat(table);
data_matrix = cell2mat(table)
Error using cell2mat (line 52)
CELL2MAT does not support cell arrays containing cell arrays or objects.

Best Answer

Hi,

Here is my answer for your question. Please read my comments near each line.

table_loaded = load('C:\Users\hingec\Downloads\ACCESS1_0.mat'); % loaded structure
your_actual_table = table_loaded.table_def; % this struct already have a table_def field and that field contains a table. 
your_timetable = table2timetable(table_loaded.table_def); % You can convert it to timetable. 
%% Once you get your table you can reach each column with dot notation like below: 
date_array   = your_timetable.YYMMDD;  % type is datetime
H_array      = your_timetable.HH;  % type is int32
Hs_tot_array = your_timetable.Hs_tot; % type is single


Tm_tot_array = your_timetable.Tm_tot; % type is single
Dm_tot_array = your_timetable.Dm_tot; % type is single
% Now manipulate them and make some convert operations because you can't
% concatanate int32, single and datetime into a double matrix.
%% For example:
H_array_converted = double(H_array); % now it is type double.
% if you don't do conversion, you can't even make mathematical operations. For example try to sum 2nd elements of arrays:
H_array(2) + Hs_tot_array(2) % this will give error. Because you can't sum int32 and single.

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MATLAB: Cell Array to table

Alberto, you are mixing metaphors.

You have a cell array containing values you want to put in a table, and (apparently) a table that is preallocated with cell variables. It looks like what you want is a table that has double variables, some with one column, some with more than one. I'm guessing, though you haven't really given any context, that you will have many of those cell arrays, and you want to assign them one at a time into each row of the table.

You have obj.Table{i}. Again, I can only guess that obj.Table is a cell array, and obj.Table{i} is a table that's been preallocated. It would help if you would either remove the parts of your code that are irrelevant to your question, or explain the code sufficiently.

In any case: Let's say t = obj.Table{i}. t is a table, and t(indx,:) is one row of that table. To assign to that one row, you need to have a table on the right-hand side. You have a cell array. So in that sense, madhan's suggestion is correct. But table actually gives you a short-cut: you can assign a one-row cell array to a row of a table, and the table on the LHS behaves "as if" you had already called cell2table. It's a convenience to save you some typing, and some execution time.

But the target has to be variables that are the right types. You say, "variable types set to cell", and there's your problem. You are, as the error msg says, trying to assign double values into cell arrays. Preallocate with double (and the right number of columns for each).

MATLAB: I have to do a single index for the North

Instead of using find, to get the index, just use boolean indexing. This allows you to combine North1 and North2 with a logical or

North1 = Dm >= 337.5 & Dm <= 360.0; % Left of north, boolean array
North2 = Dm >= 0.0 & Dm <= 22.5;    % Right of north, boolean array
Hs_N = Hs( North1 | North2 ); % | performs logical or of North1 and North2

Alternatively

North = (Dm >= 337.5 & Dm <= 360.0) | (Dm >= 0.0 & Dm <= 22.5);
Hs_N = Hs(North);

Best Answer

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MATLAB: Cell Array to table

MATLAB: I have to do a single index for the North

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