Re: list of dates

• To: mathgroup at smc.vnet.net
• Subject: [mg88391] Re: list of dates
• From: "Roger Nye" <roger.nye at actuary.ch>
• Date: Sat, 3 May 2008 06:20:06 -0400 (EDT)
• References: <fvegu1\$5e9\$1@smc.vnet.net>

```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

"Roger Nye" <roger.nye at actuary.ch> wrote in message
news:fvegu1\$5e9\$1 at smc.vnet.net...
> 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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