How to make calculations on certain cells (within a table) that meet specific criteria?

Question

I have the following code:

L_sum = zeros(height(ABC),1);
for i = 1:height(ABC)
     L_sum(i) = sum(ABC{i, ABC.L(i,4:281)});
 end

Here my table:

Problem: My sum function sums the entire row values (col. 4-281) per date whereas I only want those cells to be added whose headers are in the cell array of ABC.L, for any given date.

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X = ABC.L{1, 1}; gives (excerpt):

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Red arrow: what sum function is referencing (L of same date).

Green arrow: what I am trying to reference now (L of previous date).

Thanks for your help

Answer 1

To do that you need to first extract the columns you want to sum, and then sum them:

% some arbitrary data:
ABC = table;
ABC.L{1,1} = {'aa','cc'};
ABC.L{2,1} = {'aa','b'};
ABC.L{3,1} = {'aa','d'};
ABC.L{4,1} = {'b','d'};
ABC{1:4,2:5} = magic(4);
ABC.Properties.VariableNames(2:5) = {'aa','b','cc','d'}

% summing the correct columns:
L_sum = zeros(height(ABC),1);
col_names = ABC.Properties.VariableNames; % just to make things shorter
for k = 1:height(ABC)
    % the following 'cellfun' compares each column to the values in ABC.L{k},
    % and returns a cell array of the result for each of them, then
    % 'cell2mat' converts it to logical array, and 'any' combines the
    % results for all elements in ABC.L{k} to one logical vector:
    col_to_sum = any(cell2mat(...
        cellfun(@(x) strcmp(col_names,x),ABC.L{k},...
        'UniformOutput', false).'),1);
    % then a logical indexing is used to define the columns for summation:
    L_sum(k) = sum(ABC{k,col_to_sum});
end

Answer 2

In general, in matlab you dont need to use for loops to do simple operations like selective sums. Example:

Data=...
    [1 2 3;
    4 5 6;
    7 8 9;
    7 7 7];

NofRows=size(Data,1);
RowsToSum=3:NofRows;
ColToSum=[1,3];
% sum second dimension 2d array
Result=sum(Data(RowsToSum,ColToSum), 2)

% table mode
DataTable=array2table(Data);
Result2=sum(DataTable{RowsToSum,ColToSum}, 2)