在一系列日期中查找一个月的最后一天

尝试:

which(ave(as.numeric(ds),format(ds,"%Y%m"),FUN=function(x) x==max(x))==1)

我们可以 group_by 选择月份 max 每月的日期

library(zoo)
library(dplyr)

data.frame(ds) %>%
  group_by(month = as.yearmon(ds)) %>%
  slice(which.max(ds))


#        ds         month        
#     <date>     <S3: yearmon>
#1 2011-02-27     Feb 2011     
#2 2011-03-31     Mar 2011     
#3 2011-04-30     Apr 2011     
#4 2011-05-11     May 2011  

如果我们想要指数,我们可以

library(zoo) 
which(ds %in% unique(ave(ds, as.yearmon(ds), FUN = max)))
#[1] 27 58 88 99

功能 nth_day datetimeutils (我坚持) 允许您获取一个月的最后一天。它处理不了 NA

library("datetimeutils")
ds <- seq(as.Date("2011-02-01"), length = 100, by = "day")

nth_day(ds, n = "last")
## [1] "2011-02-28" "2011-03-31" "2011-04-30" "2011-05-11"

nth_day(ds, n = "last", index = TRUE)
## [1]  28  59  89 100

使用 endpoints 从xts包:

ds <- seq(as.Date("2011-02-01"), length=100, by="day")
ds[ds == as.Date('2011-02-28')] <- NA


library(xts)
#need to remove NA's. xts can handle dates that are not there, but doesn't like NA's
ep <- endpoints(xts(ds[!is.na(ds)], order.by = ds[!is.na(ds)]), on = "months")
ds[ep]
[1] "2011-02-27" "2011-03-30" "2011-04-29" "2011-05-10"