How to call columns from table when heading names are variable dependent

I am trying to loop through different columns in a data table in order to plot multiple different sensor readings into graphs. It seems I am unable to dot reference column names when said names are changing throughout the loop functions - is there any way to do this?

Here is what I have so far, which currently returns errors using tabular/dotParenReference that won't recognise my currentColumn, baseColumn or MaxColumn variable names as column headers:

% import WIM data and sensor names list to be read
data = readtable("Processed_WIM_09_2023_Data.xlsx");
sensornames = readtable('ESGSensorNames.xlsx');
% start separate plots for Gross and Axle weights
GrossWeightPlot = figure(1);
ax1 = axes('Parent', GrossWeightPlot);
ax1.Title.String = 'Gross Weight ESG Responses';
ax1.XLabel.String = 'Gross Vehicle Weight (kg)';
ax1.YLabel.String = 'ESG responses (microstrain)';
AxleWeightPlot = figure(2);
ax2 = axes('Parent', AxleWeightPlot);
ax2.Title.String = 'Axle Weight ESG Responses';
ax2.XLabel.String = 'Axle Weight (kg)';
ax2.YLabel.String = 'ESG responses (microstrain)';
hold on
% loop through WIM data entries
for i = 1:height(data)
    GrossWeight = data.GrossWeight;
    % find axle weight columns according to axle number
    for j = 1:data.AxlesCount(i)
        AxleColumn = sprintf('AxleWeight%s', j);
        AxleWeight = data.currentColumn(i);
        % identify sensor columns
        for k = 1:height(sensornames)
            currentSensor = sensornames(k);
            BaseColumn = sprintf('Base_%s', currentSensor);
            MaxColumn = sprinft('Max_%s', currentSensor);
            % calculate strain response (max - base)
            strainResponse = data.MaxColumn(i) - data.BaseColumn(i);
            % set plot colour and legend label according to slab
            if contains(currentSensor, '7')
                plotColour = 'b';
                legendLabel = 'Slab 7';
            elseif contains(currentSensor, '8')
                plotColour = 'r';
                legendLabel = 'Slab 8';
            elseif contains(currentSensor, '11')
                plotColour = 'g';
                legendLabel = 'Slab 11';
            end
            % plot strain responses against weights
            GWscatter = scatter(ax1, GrossWeight, strainResponse, '.', 'Color', plotColour, 'DisplayName', legendLabel);
            AWscatter = scatter(ax2, AxleWeight, strainResponse, '.', 'Color', plotColour, 'DisplayName', legendLabel);
        end
    end
end
hold off;
% set plot legends
legend(GWscatter);
legend(AWscatter);

I can attach screenshots of my data table if need be, although it is an extremely large file so doing this in a clear manner is proving difficult.

[Stephen23]

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

"Dot notation, as in T.varname or T.(expression), extracts an array from one table variable."

Answer 1

[Fangjun Jiang]

use data.(MaxColumn). This is similar to dynamic field names like below.

a.FirstColumn=1;
ColumnName='FirstColumn'

ColumnName = 'FirstColumn'

a.(ColumnName)

ans = 1

[Peter Perkins]

It's also possible to use variable indices in that syntax:

t = table([1;2;3],[4;5;6])

t = 3x2 table
    Var1    Var2
    ____    ____

     1       4  
     2       5  
     3       6  

for i = 1:width(t)
    t.(i)
end

ans = 3×1

1 2 3

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ans = 3×1

4 5 6

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●

But of course then you are not using your meaningful names.

[Steven Lord]

Or you could use curly brace indexing to extract the contents inside a table, either with names or with indices.

t = table([1;2;3],[4;5;6])

t = 3x2 table
    Var1    Var2
    ____    ____

     1       4  
     2       5  
     3       6  

N = t.Properties.VariableNames

N = 1x2 cell array
    {'Var1'}    {'Var2'}

for i = 1:width(t)
    x = t{:, N{i}} % Use names
end

x = 3×1

1 2 3

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●

x = 3×1

4 5 6

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for i = 1:width(t)
    x = t{:, i} % Use indices
end

x = 3×1

1 2 3

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x = 3×1

4 5 6

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