On Tue, 22 Dec 2009, D Kelly O'Day wrote:
I am trying to get monthly means for a daily data series using zoo(). I have found an odd problem, that seems to be caused by zoo()'s handling of leap years.
It's not really zoo's odd handling, but yours ;-) More seriously, do not use ts() with either freq = 365 or 366 to represent daily observations. zoo with "Date" index is more suitable (or the corresponding xts).
Here's my R script with 2 methods (freq=365, 366) for aggregating the daily data to monthly series: library(zoo) J_link <- "http://www.ijis.iarc.uaf.edu/seaice/extent/plot.csv"; JAXA_data <- read.table(J_link, skip = 0, sep = ",", dec=".", row.names = NULL, header = FALSE, as.is = T, colClasses = rep("numeric",4), comment.char = "#", na.strings = c("*", "-",-99.9, -9999), col.names = c("Mo", "Day", "Yr", "Extent") ) ## Subset raw data to period: Jan,2003 to Dec, 2007 JAXA <- subset(JAXA_data, JAXA_data$Yr >=2003 & JAXA_data$Yr <=2007) ## create zoo object starting Jan, 2003 - use freq's of 365 and 366 JAXA_365 <- as.zoo(ts(JAXA$Extent, start = c(2003,1,1),freq=365)) JAXA_366 <- as.zoo(ts(JAXA$Extent, start = c(2003,1,1),freq=366))
As explained above, I would use a "Date" index: JAXA_daily <- with(JAXA_data, zoo(Extent, as.Date(paste(Yr, Mo, Day, sep = "-"))) ) and then you can do JAXA_monthly <- aggregate(JAXA_daily, as.yearmon, mean, na.rm = TRUE) which should give what you expected. See zoo's package vignettes vignette(package = "zoo") for more details. hth, Z
## aggregate to yearmon using JAXA_365 & JAXA_366 zoo objects JAXA_mo_365 <- aggregate(JAXA_365, mean, by=yearmon, na.rm=T) JAXA_mo_366 <- aggregate(JAXA_366, mean, by=yearmon, na.rm=T) ## Compare last 6 records for JAXA_365 & JAXA_366 tail(JAXA_mo_365) tail(JAXA_mo_366) When I compare the two tail reports, I get Jan, 2007 for last month for JAXA_365 and Dec, 2007 for JAXA_366. What is proper freq for daily data, 365 or 366 or other? I have seen many examples that use 365 for ts, I assumed zoo() worked the same. What am I missing? -- View this message in context: http://n4.nabble.com/Using-zoo-to-aggregate-daily-data-to-monthly-means-tp977263p977263.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
