#
# xts: eXtensible time-series
#
# Copyright (C) 2008 Jeffrey A. Ryan jeff.a.ryan @ gmail.com
#
# Contributions from Joshua M. Ulrich
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
`first` <-
function(x,...)
{
UseMethod("first")
}
`first.default` <-
function(x,n=1,keep=FALSE,...)
{
xx <- try.xts(x, error=FALSE)
if(is.xts(xx)) {
xx <- first.xts(x, n=n, keep=keep)
return(reclass(xx))
}
if(is.null(dim(x))) {
if(n > 0) {
xx <- x[1:n]
if(keep) xx <- structure(xx,keep=x[(-(-n)+1):NROW(x)])
xx
} else {
xx <- x[(-n+1):NROW(x)]
if(keep) xx <- structure(xx,keep=x[1:(-n)])
xx
}
} else {
if(n > 0) {
xx <- x[1:n,]
if(keep) xx <- structure(xx,keep=x[(-(-n)+1):NROW(x),])
xx
} else {
xx <- x[(-n+1):NROW(x),]
if(keep) xx <- structure(xx,keep=x[1:(-n),])
xx
}
}
}
`first.xts` <-
function(x,n=1,keep=FALSE,...)
{
if(length(x) == 0)
return(x)
if(is.character(n)) {
# n period set
# if(!inherits(index(x),'POSIXt') && !inherits(index(x),'Date'))
# stop(paste('subsetting by date is only possible with objects having',
# 'time based indexes'))
np <- strsplit(n," ",fixed=TRUE)[[1]]
if(length(np) > 2 || length(np) < 1)
stop(paste("incorrectly specified",sQuote("n"),sep=" "))
# series periodicity
sp <- periodicity(x)
# requested periodicity$units
rpu <- np[length(np)]
rpf <- ifelse(length(np) > 1, as.numeric(np[1]), 1)
if(rpu == sp$unit) {
n <- rpf
} else {
# if singular - add an s to make it work
if(substr(rpu,length(strsplit(rpu,'')[[1]]),length(strsplit(rpu,'')[[1]])) != 's')
rpu <- paste(rpu,'s',sep='')
u.list <- list(secs=4,seconds=4,mins=3,minutes=3,hours=2,days=1,
weeks=1,months=1,quarters=1,years=1)
dt.options <- c('seconds','secs','minutes','mins','hours','days',
'weeks','months','quarters','years')
if(!rpu %in% dt.options)
stop(paste("n must be numeric or use",paste(dt.options,collapse=',')))
dt <- dt.options[pmatch(rpu,dt.options)]
if(u.list[[dt]] > u.list[[sp$unit]]) {
# req is for higher freq data period e.g. 100 mins of daily data
stop(paste("At present, without some sort of magic, it isn't possible",
"to resolve",rpu,"from",sp$scale,"data"))
}
ep <- endpoints(x,dt)
if(rpf > length(ep)-1) {
rpf <- length(ep)-1
warning("requested length is greater than original")
}
if(rpf > 0) {
n <- ep[rpf+1]
xx <- (x[1:n])
if(keep) xx <- structure(xx,keep=x[(ep[-(-rpf)+1]+1):NROW(x)])
return(xx)
} else {
n <- ep[-rpf+1]+1
xx <- (x[n:NROW(x)])
if(keep) xx <- structure(xx,keep=x[1:(ep[-rpf+1])])
return(xx)
}
}
}
if(length(n) != 1) stop("n must be of length 1")
if(n > 0) {
n <- min(n, NROW(x))
xx <- x[1:n]
if(keep) xx <- structure(xx,keep=x[(-(-n)+1):NROW(x)])
xx
} else {
if(abs(n) >= NROW(x))
return(x[0])
xx <- x[(-n+1):NROW(x)]
if(keep) xx <- structure(xx,keep=x[1:(-n)])
xx
}
}
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