loadChannel

Syntax

ds.loadChannel(channelName)

Description

ds.loadChannel(channelName) Loads channel data for the channels given by channelName from the datasource's *.MAT file into memory. channelName can be a string if only one channel needs to be loaded or a cell array of channel names to load multiple channels.

Note: ds is a single datasource not the array of datasources typically returned by dm.getDatasource

Using loadChannel

The datasource returned by ds = dm.getDatasource preload the channel data from their *.MAT file into memory rather that data is only loaded when requested by loadChannel, so as to not waste time loading unnecessary data into the working memory.

Additionally when using loadChannel it is advisable to load all channels at once rather than load them one at a time. As loading channel data all at once will be on average 2.17 times faster than loading channels one by one, as demonstrated by the following script:

%Grab a datasource
dm = Datamaster;
ds = dm.getDatasource('limit', 1);

%Initalize counter arrays
one = []; all = [];

%Run multiple iterations
for i = 1:1000
    %Clear datasource
    ds.clearData
    
    %Pick a method at random
    if rand > 0.5
        tic
        ds.loadChannel('Engine_RPM')
        ds.loadChannel('Throttle_Pos')
        ds.loadChannel('Manifold_Pres')
        one(end+1) = toc;
    else
        tic
        ds.loadChannel({'Engine_RPM';'Throttle_Pos';'Manifold_Pres'})
        all(end+1) = toc;
    end
end

%Report Results
fprintf('Load all at once: %f stdev: %f n: %d\n', mean(all), std(all), length(all));
fprintf('Load one by one: %f stdev: %f n: %d\n', mean(one), std(one), length(one));
fprintf('Speed up of: %1.2fx\n', mean(one) /mean(all));

This speed up can become significant when conducting analysis using hundreds of datasources, especially when the Datastore is not located on a local drive.

Note: ds.getChannel will call ds.loadChannel as needed and thus the use of ds.loadChannel is optional. However this is not advised due to the significant speed penalty.