MATLAB: How to convert numerical dates to conventional dates

converting datesdatestrimportfilestocksxlswrite

I have imported a spreadsheet historic stock prices for a stock (ticker CHK) into Matlab using the importfile function. The goal is to plot the price movements, and volume movements and to show the conventional dates labeled on the x-axis.
When I imported the spreadsheet, the Date column converted to a number (for example August 17, 2011 reads 40772). I converted the numerical date to a conventional date and wrote it into Excel using the datestr function, and the xlswrite function. The conventional date can now be seen on the spreadsheet outside of Matlab; however, the variable cDate (conventional date) in the workspace shows this symbol { }cDate, instead of a grid like the other variables and I can't plot it.
Here are the functions I've used to get this far.
     importfile('chk.xls');
     cDate = Date;
     cDate = x2mdate(cDate, 0);
     str = datestr(cDate, 1);
     cDt = cellstr( str );
I want the cDt cell array to convert into a double vector of the same size. I.e, in the workspace, all the variables are a double vector of the same size < 254×1 double >, except cDt, which reads < 254×1 cell >. I am not sure what I need to do to accomplish this. Essentially I want to graph a stock price movement from Aug 31, 2011 to Aug 31, 2012 and I want the x-label to read the day, month etc, versus the Matlab serial number.

Best Answer

The Excel datetime-number is not the same as the serial date number of Matlab
    >> datestr( 40772, 1 )
    ans =
    18-Aug-0111
    >>
The pivot-year of Excel is 1900 and of Matlab is 0. You need to look it up.
The use of "ans" as temporary variable is not a good practice.
    datestr(cDate, 1);
    cellstr(ans);
    cDate = ans;
Someone discovered that it saves a couple of bytes and now it has become common practice in Cody. However, outside Cody this is much better
    str = datestr(cDate, 1);
    cDate = cellstr( str );
It is easier to debug code if you do not reuse the temporary variables. Thus
    str = datestr( cDate, 1 );
    cDt = cellstr( str );
I might not have answered your question.
--- In response of comment 1 ---
Matlab documentation says:
    Working with Serial Date Numbers
    A serial date number represents a calendar date as the number 
    of days that has passed since a fixed base date. 
    In MATLAB, serial date number 1 is January 1,0000. MATLAB also 
    uses serial time to represent fractions of days beginning at 
    midnight; for example, 6 p.m. equals 0.75 serial days. So the 
    string '31-Oct-2003, 6:00 PM' in MATLAB is date number 731885.75.
Excel online help says:
    Excel stores dates as sequential serial numbers so that they can be
    used in calculations. By default, January 1, 1900, is serial number 1,
    and January 1, 2008, is serial number 39448 because it is 39,448 days
    after January 1, 1900.
.
A test in Matlab
>> datenum('2008-01-01','yyyy-mm-dd')-datenum('1900-01-01','yyyy-mm-dd')
ans =
       39446
thus I have to add 2. Now you can calculate and write a number to Excel.
However, you need to set the "Number format" of the cell to "Short date". I don't know how to do that with Matlab code.
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