# Can this for-loop code get faster in some way?

3 views (last 30 days)
Martin on 5 Oct 2019
Commented: darova on 6 Oct 2019
I got a big result table named resTbl.
There I need for each row to grab a timestamp (posix time) and construct a period interval vector (I use a constant, ts_length, to construct this).
Then I need to find all those in period_interval that are represented in the variable data (column 2), and take the sum of those in data (column 7).
The below code works as I want it to:
for i = 1 : size(resTbl ,1)
period_interval = resTbl(i,2) : 60000 : resTbl(i,2) + ts_length;
[hd, he] = ismember(period_interval,data(:,2));
resTbl(i,10) = sum(data(he(hd),7));
end
The problem is that it is slow since resTbl has many rows. Does anyone have a suggestion how to make it faster?
per isakson on 5 Oct 2019

darova on 5 Oct 2019
Edited: darova on 5 Oct 2019
Maybe ismember function can be replaced:
dt = 60000;
period_interval = 0 : dt : ts_length;
n = length(period_interval);
for i = 1 : size(resTbl ,1)
cond = ~mod( data(:,2)-resTbl(i,2),dt ); % multiple by 60 000
mult = (data(:,2)-resTbl(i,2))/dt;
ind = (0 <= mult & mult <= n) & cond; % (0 <= multiplier <= n) and multiple by 60 000
% [hd, he] = ismember(period_interval,data(:,2));
resTbl(i,10) = sum(data(ind,7));
end
darova on 6 Oct 2019
2 million rows and 7 columns
Maybe time is a price in this case

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