select selected numeber of rows from an huge array

Hi,

I need to select 365 (366,:) rows from array of [3652500 x 2] and write a matrix [366 x 10000]. Can somebody help me with that. I am new to MATLAB.

Thanks in advance.

[Star Strider]

What do you mean by ‘365 (366,:) rows’?

You will have to delete 3.6550e+006 elements from your [3652500x2] matrix to create your [366x10000] matrix. What elements get included? What elements get left out?

[Damith]

hi,

I need to extract elements from row 1 to 366, 367 to 731..and so on and write to a (366 x 10000) matrix. I am not removing any row or columns but its sort of an arranging in a different way. Hope this helps.

[Cedric]

3652500 is a multiple of neither 365 nor 366; could you build an example with e.g. a 6x2 input array?

[dpb]

>>  (3652500*2)==(366*10000)
ans =
   0
>> num2str((3652500*2)/366,'%.5f')
ans =
19959.01639
>>

Don't fit.

doc reshape % but will have to be commensurate sizes

[Walter Roberson]

Your first dimension is being reduced by a factor of about 10000, but your second dimension is being increased by a factor of 5000 (10000 / 2). Where is the remaining data to go?

Answer 1

[per isakson]

There are a couple of magic numbers in your question. I guess it is the number of days in a year. "366" is leap year.

    >> M = cssm;
    >> whos M

returns

    Name        Size                  Bytes  Class     Attributes
    M         366x10000            29280000  double

where

    function M02 = cssm
        N01 = 3652500;
        N02 = 1e4;
        M01 = randi( [1,17], [N01,2] );
        M02 = nan( 366, N02 );
        x01 = 1;
        for jj = 1 : N02
            if rem( jj, 4 ) >= 1
                x02 = x01 + 365 - 1;
                M02(1:365,jj) = M01( x01:x02, 1 ); 
                x01 = x02+1;
            else % leap year
                x02 = x01 + 366 - 1;
                M02(1:366,jj) = M01( x01:x02, 1 ); 
                x01 = x02+1;
            end
        end
    end

.

Comment: I chose to build the new array from the first column of your array. You can easily modify the code to use the second column or both.

.

Answer to comment:

I downloaded 0001.txt, but I still lack information

• What is the first column of whole numbers? It is not time information.
• Which of the first and second column shall be included in the result?
• There is no way to decide which data belongs to leap years.

Try

    M02 = cssm;
    whos M02

which returns

    Name        Size                  Bytes  Class     Attributes
    M02       366x10000            29280000  double

where

    function    M02 = cssm( varargin )
        narginchk( 0, 1 )
        if nargin == 1
            filespec = varargin{1};
        else
            filespec = 'h:\m\cssm\0001.txt';
        end
        fid = fopen( filespec, 'r' );
        cac = textscan( fid, '%f%*f%*f%f' );
        fclose( fid );
        M01 = cat( 2, cac{:} );
        M02 = cssm_( M01 );
    end
    function    M02 = cssm_( M01 )
        N02 = 1e4;
        M02 = nan( 366, N02 );
        x01 = 1;
        for jj = 1 : N02
            if rem( jj, 4 ) >= 1
                x02 = x01 + 365 - 1;
                M02(1:365,jj) = M01( x01:x02, 2 ); 
                x01 = x02+1;
            else % "leap" year
                x02 = x01 + 366 - 1;
                M02(1:366,jj) = M01( x01:x02, 2 ); 
                x01 = x02+1;
            end
        end
    end

[Damith]

Hi,

I think you sort of got I wanted to, so I have this array x = 3652500 x 2. How can I make use of your code to create 366 x 10000 matrix. After every 4 years, I need to extract 366 rows but for other years 365. But finally my matrix will look like 366 x 10000.

[dpb]

Need to check for the odd year that isn't leap year -- 2000, for one relatively recent...it's the 400-yr exception to the rule.

[per isakson]

@Damith, My code does that. Did you run it? The column of ordinary years are padded with a NaN to give 366 rows. The line

    if rem( jj, 4 ) >= 1

need to be replaced by

    if not( leapyear( yy ) )

The Aeronautic Toolbox contains a function named, leapyear. The File Exchange contains a few similar functions. You didn't provide time info together with the array x.

.

@dpb, The year 2000 is a leap year because it is an exception to the exception

[Damith]

@per isakson,

I tried to run your code but did not understand where to insert my data array. I have attached the link to download 0001.txt file for you to have a look (see below). Basically i am reading a text file (0001.txt) the 1st and 4th column. That's why I said I have an array of 3652500 x 2. I sort of understand your code but don't know how to modify it. (I can read this txt file and I found the MATLAB code for that)

Thanks again.

Data file download

[per isakson]

@Damith, I added to the answer above. Use the debugging tools to analyze the behavior of the new function, cssm

Here are some links on debugging in Matlab

• Debugging in MATLAB
• Debugging session
• Debugging Approaches

[Damith]

@ per isason,

Thanks. I figuerd it out using ur code. Many thanks again.