Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: list of dates

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88414] Re: list of dates
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Mon, 5 May 2008 06:10:29 -0400 (EDT)

On 5/3/08 at 6:20 AM, roger.nye at actuary.ch (Roger Nye) wrote:

>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.

Your code is doing quite a bit more than what is needed.

Bob Hanlon's solution (which I like better than what I had
suggested) is easily made to handle lists as follows:

myDate[x_String] :=
   DateDifference["1900-01-01", x, "Year"][[1]];

SetAttributes[myDate, Listable]

In[3]:= myDate[{"1963-01-01", "1985-07-01"}]

Out[3]= {63,85.4959}

However, this code may not be all that much faster than your
code above. The problem is DateDifference is designed to handle
a fairly wide range of date formats. I believe the overhead
involved to allow a wide range of date formats is the main slow down.

Here is a version that gives about a factor of 2 improvement on
my machine

In[5]:= newDate[x_String] :=
  DateDifference[{1900, 1, 1}, ToExpression /@ StringSplit[x, "-"],
    "Year"][[1]]

In[6]:= SetAttributes[newDate, Listable]

In[7]:= newDate[{"1963-01-01", "1985-07-01"}] // Timing

Out[7]= {0.025224,{63,85.4959}}

comparing:

In[8]:= myDate[{"1963-01-01", "1985-07-01"}] // Timing

Out[8]= {0.053429,{63,85.4959}}


  • Prev by Date: Re: Wolfram Workbench user experiences
  • Next by Date: RE: Fit data with range
  • Previous by thread: Re: Re: list of dates
  • Next by thread: Re: list of dates