From jens.oehlschlaegel-akiyoshi@mdfactory.de  Fri Feb 11 13:21:44 2000
From: jens.oehlschlaegel-akiyoshi@mdfactory.de (=?iso-8859-1?Q?Jens_Oehlschl=E4gel-Akiyoshi?=)
Date: Fri, 11 Feb 2000 14:21:44 +0100
Subject: [Rd] astonishing memory phenomenon
In-Reply-To: <200002111253.MAA24081@toucan.stats.ox.ac.uk>
Message-ID: <000701bf7492$f169e740$a9021aac@joelschlaegel>



Thanks for the explanation Brian!

> You only have one character data object, of length 0, 4096, 8192,>and lots
of references to it.
> You don't need multiple copies of the same data.

This (definitely clever) behaviour of R makes it more difficult to decide,
HOW to import large amounts of data, if the data type is DATE. Dates could
be imported as CHARACTER or as DOUBLE (chron-objects).

Memory requirements of chron would be approx   n*8 Bytes
Memory requirements of character dates like "01/01/2000" would be n*4 + u*10
Memory requirements of character times like "23:03:20" would be n*4 + u*8
Memory requirements of character date-times like "01/01/2000 23:03:20" would
be n*4 + u*19
where n=no of cases and u=no of unique values

Concerning date-times from

  n*8 < n*4 + u*19

we get

  n/u < 4.75

as a condition for the chron object beeing smaller than a character
representation, thus the answer is: IT DEPENDS.

BTW: Is there any specific reason that currently we cannot have chron
objects as columns of data.frames?

Regards


Jens Oehlschlgel-Akiyoshi

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[Rd] astonishing memory phenomenon
=?iso-8859-1?Q?Jens_Oehlschl=E4gel-Akiyoshi?=