查找本月的第一个星期二 [英] Find first Tuesday of Month

问题描述

我正在尝试编写一个将日期向量作为输入并返回日期向量的函数-其中输出是与输入日期匹配的月份的第一个星期二的日期.

I am trying to write a function which takes a vector of dates as an input and returns a vector of dates -- where the output is the date of the first Tuesday of the month which matches the input date.

所以 2012-11-19 -> 2012-11-06 等

我在一次约会中就取得了一些成功，但无法归纳为向量案例.有人可以帮忙吗?

I have had some success with a single date, but have not been able to generalise to the vector case. Could someone please help?

这是我到目前为止所拥有的:

This is what I have so far:

firstTuesday <- function(tt){
  ct <- as.POSIXct(tt)
  lt <- as.POSIXlt(tt)
  firstOf <- as.POSIXlt(ct - 60*60*24* (lt$mday - 1))
  if (firstOf$wday > 2) 
  {
    adjDays <- (9 - firstOf$wday)
    firstTues <- as.POSIXlt(as.POSIXct(firstOf) + 60*60*24*adjDays)
  }
  else {
    adjDays  <- (2 - firstOf$wday)
    firstTues <- as.POSIXlt(as.POSIXct(firstOf) + 60*60*24*adjDays)
  }
  return(firstTues)
}

哪个日期适用于单个日期: firstTuesday(Sys.Date())，但对日期向量产生了垃圾(由于 if 不是矢量化控件的问题，运营商，我认为).

Which works for a single date: firstTuesday(Sys.Date()) but yielded junk for vectors of dates (due to issues with if not being a vectorised control operator, i think).

我通过使用索引避开了我有限的理解.以下代码似乎可以解决问题.

I got around my limited understanding by using indexing. The following code seems to do the trick.

firstTuesday <- function(tt){
  ct <- as.POSIXct(tt)
  lt <- as.POSIXlt(tt)
  firstOf <- as.POSIXlt(ct - 60*60*24* (lt$mday - 1))
  firstTue <- as.POSIXct(firstOf)
  idx <- firstOf$wday > 2
  firstTue[idx]  <- as.POSIXct(firstOf[idx]) + 60*60*24*(9 - firstOf$wday[idx])
  firstTue[!idx]  <- as.POSIXct(firstOf[!idx]) + 60*60*24*(2 - firstOf$wday[!idx])
  return(firstTue)
}

推荐答案

这使用lubridate并使逻辑更简单.给定一个日期向量，第二个函数将返回一个字符向量，类似于您的输入.您可以根据自己的需要进行更改.

This uses lubridate and makes the logic a little simpler. Given a vector of dates the second function will return a vector of characters, similar to your input. You can change things around to suit your needs.

library(lubridate)

getTuesday = function(x) {
    date = ymd(x)
    first = floor_date(date,"month")
    dow = sapply(seq(0,6),function(x) wday(first+days(x)))
    firstTuesday = first + days(which(dow==3)-1)
    return(firstTuesday)
}

getMultipleTuesdays = function(y) {
    tmp = lapply(y, getTuesday)
    tmp = lapply(tmp, as.character)
    return(unlist(tmp))
}

编辑

样本输入/输出

getMultipleTuesdays(c("2012-11-19","2012-11-19","2011-01-15"))
[1] "2012-11-06" "2012-11-06" "2011-01-04"

这篇关于查找本月的第一个星期二的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！