www.gusucode.com > matlab 案例源码 matlab代码程序 > matlab/DelayedEvaluationOfTallArraysExample.m
%% Evaluate Deferred Tall Array Calculation % Create a datastore for the |airlinesmall.csv| data set. Select a subset % of variables to work with, and treat |'NA'| values as missing data so % that |datastore| replaces them with |NaN| values. Convert the datastore % into a tall table. varnames = {'Year','ArrDelay','UniqueCarrier'}; ds = datastore('airlinesmall.csv', 'TreatAsMissing', 'NA',... 'SelectedVariableNames',varnames); T = tall(ds) %% % Calculate the size of the tall table. sz = size(T) %% % MATLAB(R) does not immediately evaluate most operations on tall arrays. % Instead, MATLAB remembers the operations you perform as you enter them % and optimizes the calculations in the background. % % When you use |gather| on an unevaluated tall array, MATLAB executes all % of the queued operations using the minimum number of passes through the % data. This optimization greatly reduces the execution time of large % calculations. For this reason, you should use |gather| only when you need % to see a result. %% % Use |gather| to execute the calculation and collect the result into % memory. S = gather(sz)