tallArray sorting and plot error

Issue description:

I converted a large amount of files into .mat files and create datastore and tallArray to make some plots. What I would like to do is to create a tallArray and trim the data to only have the rows and columns that I need and plot them.

Matlab script

clear all;

fileToPlot = '12C_011_Matfiles';
parentpath = 'You can just put a directoray here to /12C Mat files/';

% Create tall array of the fileToPlot
ds = datastore(strcat(parentpath, fileToPlot));
tallArray = tall(ds);
% Only get the two columns of data and rows when the two conditions tallArray.State='D' and tallArray.ES>1 are both met. 
tt.Cycles = gather([tallArray.State{:}] == 'D' & tallArray.ES>1, tallArray.Cyc_);
tt.DchAh = gather([tallArray.State{:}] == 'D' & tallArray.ES>1, tallArray.Amp_hr);

% Plot the figure only for the cycles <=200
figure (1)
plot(Cycles<=200,DchAh)

Error:

Indexing expressions of the form T{...,...} are not supported for tall arrays.

when I changed the code from

tt.Cycles = gather([tallArray.State{:}] == 'D' & tallArray.ES>1, tallArray.Cyc_);

to

tt.Cycles = gather(tallArray.State(:) == 'D' & tallArray.ES>1, tallArray.Cyc_);

I got new errors below:

Undefined operator '==' for input arguments of type 'cell'.

Error in ==

Error in CL_plots_NJ (line 9)

tt.Cycles = gather(tallArray.State(:) == 'D' & tallArray.ES>1, tallArray.Cyc_);

Error in tall/gather (line 50)

[varargout{:}, readFailureSummary] = iGather(varargin{:});

Error in CL_plots_NJ (line 9)

tt.Cycles = gather(tallArray.State(:) == 'D' & tallArray.ES>1, tallArray.Cyc_);

Answer 1

[Rick Amos]

Instead of converting State to a character vector, I would recommend using one of the string utilities. These are all supported by tall array:

tt.Cycles = gather(strcmp(tallArray.State, 'D') & tallArray.ES>1, tallArray.Cyc_);

Or, if you are using R2018b or later, you can use the string type. Strings are an improved version of cell array of character vector and support equality. To create a string as opposed to a character vector, use double quotes:

tt.Cycles = gather(tallArray.State == "D" & tallArray.ES>1, tallArray.Cyc_);