查找最近的星期一数据帧 [英] Find most recent Monday for a dataframe

问题描述

我有一个数据框对象，其中的字段中有一个日期：

  df $ dates 
  

我需要添加一个周开始列，即

  df [，'WeekStart'] = manipulation 
  

周的开始时间是该周的星期一的日期。即：今天是24/09/15，星期四，将有一个21的条目。下个星期二，01/10/15，将是'28 - 禁止'。

我看到有一个 weekday（）函数将会将一天变成一个星期，但是如何处理这个最近的星期一？

解决方案

Simples：

  dates< ;-( Sys.Date ）+1：30）
 week.start<  -  as.Date（sapply（dates，function（d）{return（d +（-6  -  as.POSIXlt（d）$ wday %% -7） ）}），origin =1970-01-01）
  

并运行为

  d<  -  data.frame（dataes = dates，monday = week.starts）
  / pre> 
 
 
给
  dataes monday 
 1 2015 -09-25 2015-09-21 
 2 2015-09-26 2015-09-21 
 3 2015-09-27 2015-09-21 
 4 2015-09-28 2015 -09-28 
 5 2015-09-29 2015-09-28 
 6 2015-09-30 2015-09-28 
 7 2015-10-01 2015-09-28 
 8 2015-10-02 2015-09-28 
 9 2015-10-03 2015-09-28 
 10 2015-10-04 2015-09-28 
 11 2015-10-05 2015-10-05 
 12 2015-10-06 2015-10-05 
 13 2015-10-07 2015-10-05 
 14 2015-10- 08 2015-10-05 
 15 2015-10-09 2015-10-05 
 16 2015-10-10 2015-10-05 
 17 2015-10-11 2015-10- 05 
 18 2015-10-12 2015-10-12 
 19 2015-10-13 2015-10-12 
 20 2015-10-14 2015-10-12 
 21 2015-10-15 2015-10-12 
 22 2015-10-16 2015-10-12 
 23 2015-10-17 2015-10-12 
 24 2015-10- 18 2015-10-12 
 25 2015-10-19 2015-10-19 
 26 2015-10-20 2015-10-19 
 27 2015-10-21 2015-10- 19 
 28 2015-10-22 2015-10-19 
 29 2015-10-23 2015-10-19 
 30 2015-10-24 2015-10-19 
  
类似的方法，例如：
 ＃data 
d<  -  data.frame（date = as.Date（c（20/09/2015，24/09/2015，28/09/2015， 01/10/2015），％d /％m /％Y））
 
＃获取星期一
d $ WeekStart<  -  d $ date  -  6  - （as.POSIXlt （d $ date）$ wday %% -7）
 
d 
＃result 
＃date WeekStart 
＃1 2015-09-20 2015-09-14 
＃2 2015-09-24 2015-09-21 
＃3 2015-09-28 2015-09-28 
＃4 2015-10-01 2015-09-28 
  
 
I have a dataframe object, and among the fields in it, I have a dates:
df$dates
I need to add a column which is 'Week Starting', i.e.
df[,'WeekStart']= manipulation
Where the week start is the date of the Monday of that week. i.e.: today is Thursday 24/09/15, would have an entry as '21-Sept'. Next thursday, 01/10/15, would be '28-Sept'.

I see that there is a weekday() function which will convert a day into a week-day, but how can I deal with this most recent monday?
解决方案
Simples:
dates <-(Sys.Date()+1:30)
week.starts <- as.Date(sapply (dates, function(d) { return (d + (-6 - as.POSIXlt(d)$wday %% -7 ))}), origin = "1970-01-01")
and running as
d <- data.frame(dataes=dates, monday=week.starts)
gives
       dataes     monday
1  2015-09-25 2015-09-21
2  2015-09-26 2015-09-21
3  2015-09-27 2015-09-21
4  2015-09-28 2015-09-28
5  2015-09-29 2015-09-28
6  2015-09-30 2015-09-28
7  2015-10-01 2015-09-28
8  2015-10-02 2015-09-28
9  2015-10-03 2015-09-28
10 2015-10-04 2015-09-28
11 2015-10-05 2015-10-05
12 2015-10-06 2015-10-05
13 2015-10-07 2015-10-05
14 2015-10-08 2015-10-05
15 2015-10-09 2015-10-05
16 2015-10-10 2015-10-05
17 2015-10-11 2015-10-05
18 2015-10-12 2015-10-12
19 2015-10-13 2015-10-12
20 2015-10-14 2015-10-12
21 2015-10-15 2015-10-12
22 2015-10-16 2015-10-12
23 2015-10-17 2015-10-12
24 2015-10-18 2015-10-12
25 2015-10-19 2015-10-19
26 2015-10-20 2015-10-19
27 2015-10-21 2015-10-19
28 2015-10-22 2015-10-19
29 2015-10-23 2015-10-19
30 2015-10-24 2015-10-19
Similar approach, example:
# data
d <- data.frame(date = as.Date( c("20/09/2015","24/09/2015","28/09/2015","01/10/2015"), "%d/%m/%Y"))

# get monday
d$WeekStart <- d$date - 6 - (as.POSIXlt(d$date)$wday %% -7)

d
# result
#         date  WeekStart
# 1 2015-09-20 2015-09-14
# 2 2015-09-24 2015-09-21
# 3 2015-09-28 2015-09-28
# 4 2015-10-01 2015-09-28


                        
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