From stephen.mcintyre at utoronto.ca  Wed Apr 30 15:00:04 2008
From: stephen.mcintyre at utoronto.ca (stephen.mcintyre at utoronto.ca)
Date: Wed, 30 Apr 2008 15:00:04 +0200 (CEST)
Subject: [Rd] apply and monthly time series (PR#11352)
Message-ID: <20080430130004.74F412834154@mail.pubhealth.ku.dk>

Full_Name: Stephen McIntyre
Version: 2.7
OS: Windows XP
Submission from: (NULL) (99.231.2.44)


When I use the apply function to calculate a trend for a matrix of monthly time
series, it yields a different answer than when the trend is calculated one at a
time (by a factor of 12) rather than the identical answer as it should. Here's
an example:
 
download.file("http://www.climateaudit.org/data/models/monthly.tab","temp.dat",mode="wb")
load("temp.dat")
trend= function(x)  lm(x~c(time(x)))$coef[2]
b= apply(monthly,2,trend)
a= c(trend(monthly[,1]),trend(monthly[,2]),trend(monthly[,3]))
a/b  #12 12 12



[Rd] apply and monthly time series (PR#11352)
stephen.mcintyre at utoronto.ca