Preallocation not helping with speed; actxserver

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Robert Dylans
Robert Dylans 2015-9-1
评论： Robert Dylans 2015-9-2
I have a folder of 500 separate Excel files (.csv to be specific). I'm reading a specific data range from them. My main problem is that it's taking longer than I would expect. Originally with xlsread I was taking ~200 seconds. I've recently learned of using actxserver and have cut down to ~50 seconds. I'm trying to preallocate memory for it, but I've noticed that the duration is exactly the same whether I do this or not.
z=zeros(3452,1);
for i=1:500
high{i}=z;
end
tic
folder='F:\Program Files\Historical\daily';
files=dir(fullfile(folder,'*.csv'));
e=actxserver('Excel.Application');
for k=1:numel(files)
waitbar(k/numel(files),progress);
ExcelWorkbook=e.workbooks.Open(fullfile(folder,files(k).name));
range=ExcelWorkbook.ActiveSheet.Range('E1:E3452');
high{k}=range.Value;
end
toc
Am I formatting the preallocation wrong? Or am I missing something else? Or is my computer just slow?
Thanks for any help.

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采纳的回答

Image Analyst
Image Analyst 2015-9-1
They're simple csv files, not complicated workbooks. Have you tried simply using csvread()? Maybe that will be faster since there's no overhead of trying to launch and shutdown Excel.
  1 个评论
Robert Dylans
Robert Dylans 2015-9-2
Yes... thank you. Didn't realize what a significant different there was. Cut down from 50 seconds to 4 seconds.
Edited code, in case anybody finds this in a future search...
Had to edit a bit since csvread handles different length files differently than xlsread. Each file had a different number of rows. In this case I wanted them aligned/oriented with the last data point being the last row in each column.
tic
folder='F:\Program Files\Historical\daily';
files=dir(fullfile(folder,'*.csv'));
datapoints=3926; %Did a previous scan to find longest file
numfiles=numel(files);
high=zeros(datapoints,numfiles);
for k=1:numfiles
data=csvread(fullfile(folder,files(k).name));
high((datapoints-length(data)+1):datapoints,k)=data(:,1); %import column 1 only
end
toc

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