subsetting dates in a matrix

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Cagdas Ozgenc 2013-11-1

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评论： Cedric 2013-11-1

Hello,

I have a time series in a matrix and first column is serial date numbers (up to millisecond precision), and other columns my samples. I would like to get those rows that belong to for example '12-Oct-2012'. I couldn't figure out how to write the logical operator to get a slice of this matrix. I would like to hopefully avoid some sort of slow string comparison.

Thanks in advance

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Azzi Abdelmalek 2013-11-1

Show the two first rows of your data

Cagdas Ozgenc 2013-11-1

编辑：Cagdas Ozgenc 2013-11-1

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735236.4590277778  1.4264e+03  1.4272e+03  1.4217e+03
735236.4597222222  1.4237e+03  1.4252e+03  1.4234e+03
735236.4604166667  1.4247e+03  1.4267e+03  1.4244e+03

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Answer 1

Cedric 2013-11-1

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编辑：Cedric 2013-11-1

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You already have serialized/numeric time stamps in you array, so just convert date boundaries to numeric, and compare numbers: assuming your array is named data..

 lb_incl = datenum( '12-Oct-2012', 'dd-mmm-yyyy' ) ;
 ub_excl = datenum( '13-Oct-2012', 'dd-mmm-yyyy' ) ;
 id = data(:,1) >= lb_incl & data(:,1) < ub_excl ;
 dailyMean = mean( data(id,2) ) ;

or

dailySlice = data(id,2:end) ;

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Cagdas Ozgenc 2013-11-1

Thanks. In this scenario this is a good option.

Cedric 2013-11-1

You're welcome.

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Answer 2

Azzi Abdelmalek 2013-11-1

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If A is your cell array

c1=cellstr(datestr(A(:,1),'dd-mm-yyyy'))
idx=ismember(c1,'12-10-2012')
out=A(idx,:)

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Cagdas Ozgenc 2013-11-1

Takes forever on my dataset of million lines. It converts all serial numbers back to string and then compares those strings. Then gets the indices. Then gets the data.

Thanks anyways

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