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Re: list of dates

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  • Subject: [mg88391] Re: list of dates
  • From: "Roger Nye" <roger.nye at>
  • Date: Sat, 3 May 2008 06:20:06 -0400 (EDT)
  • References: <fvegu1$5e9$>

Thanks for your suggestions.

A key aspect of the problem is that the dates are a list, so I want to be 
able to operate on them as a list.
The approximation of leap years does not concern me, although the year has 
to be correct (i.e. 1st Jan of year xx must be xx.0, not xx-1.997).

Adapting your suggestions and after much struggle (I am new to Mathematica), 
I came up with this
("date" is the list of dates input, "t" is the list of values output):

n = Length[date];
year = Transpose[Map[DateList, date]][[1]];
days =  Table[DateDifference[{year[[i]]}, date[[i]]], {i, 1, n}];
t = year - 1900 + days / 365.24;

which does what I wanted (thanks).
It is however very slow.  It takes a couple of minutes for 15,000 dates.
All the other software I have used for a similar calculation (Excel, Stata) 
does it in a split second.

Is there a much more efficient method?

Many thanks

"Roger Nye" <roger.nye at> wrote in message 
news:fvegu1$5e9$1 at
> Hi,
> I have a list of dates in the format YYYY-MM-DD and I want to convert them
> to a decimal value, so 1963-01-01 goes to 63.0 and 1985-07-01 goes roughly
> to 85.5.
> Any suggestions on the best way to do this?
> Many thanks
> Roger

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