How to make conditional calculations in a table using loop mechanisms? - matlab

Question

I have the following table ('ABC'):
Goal: For each date, create 2 new variables (e.g. 'LSum' and 'USum'). 'LSum' should calculate the sum of all cell values across the column universe (4-281), but only with those values whose header is in the cell array of ABC.L, for that specific date. In the same fashion, 'USum' should calculate the sum of all cell values across the columns, but only with those values whose header is in the cell array of ABC.U, for that specific date.
% load content
load ('ABC.mat');
% run through every date, starting from the top
for row=1:size(ABC,1);
% for-loop for 'L' that determines for what specific cells (of col. 4-281) the following calculation has to be done: how?
% for-loop for 'U' that determines for what specific cells (of col. 4-281) the following calculation has to be done: how?
% now generate new variables
LSum = sum(); % But how can I use if clause here to select only eligible cells that enter into the sum calculation?
USum = sum(); % Same problem here as LSum
end;
% Concatenate table ABC and the newly formed variables into 1 table
ABC = [ABC(:,1:3) LSum USum ABC(:,3+1:end)];
Thanks for your help, especially for the looping through date and the cell arrays of 'L' and 'U' at the same time.

Answer 1

Possible way how to avoid loops is to utilize rowfun() function. Suppose we have table similar to yours.
Augment the table by column with table variable names.
tb = horzcat(tb,repmat({tb.Properties.VariableNames},1,height(tb))');
Define function which is applied onto every row.
function out = selectiveSum(varargin)
[~,~,sumColsId] = intersect(varargin{2},varargin{end});
out = sum(cell2mat(varargin(sumColsId)));
end
Run rowfun().
sums = rowfun(#selectiveSum,tb);
The function deals just with one selector array (L column). Add the second one and let the selectiveSum() return 1x2 vector.