How to get week starting date from a date in R

Question

I have a dataset with a column containing dates. I want to find the week starting dates for those date values.

I get the week number using week function from lubridate. For example,

week(as.Date("04/20/2017", "%m/%d/%Y"))

#Solution
[1] 16

Instead of weeknum, is there a way to get the starting date of the week? In this case I am expecting either "04/16/2017" or "04/17/2017". I am not very particular if the week starts from Sunday or Monday. I looked at this question, but didn't get much from it.

Another way, with data.table: `round(as.IDate("04/20/2017", "%m/%d/%Y"), "week")` — Frank, Apr 20 '17 at 14:04

score 32 · Accepted Answer · edited Feb 10 '21 at 01:25

32

Use the floor_date function from the lubridate package.

library("lubridate")
floor_date(as.Date("04/20/2017", "%m/%d/%Y"), unit="week")

edited Feb 10 '21 at 01:25

Khaynes

1,976
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answered Apr 20 '17 at 13:50

Vamsi Prabhala

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4

Make you add `library(lubridate)` before running `floor_date` – Steve Strates Mar 30 '19 at 22:44
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worth mentioning that can also force the week to start on a Monday with `floor_date(x, unit = 'week', week_start = 1)` ? – r.bot Oct 13 '22 at 15:42

score 9 · Answer 2 · answered Apr 20 '17 at 13:51

9

You can use below

as.Date(format(as.Date("04/20/2017", "%m/%d/%Y"),"%Y-%W-1"),"%Y-%W-%u")
[1] "2017-04-17"

answered Apr 20 '17 at 13:51

Erdem Akkas

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I'm not sure whether it's an issue with how `format` works or just its use here, but this doesn't work for all dates; for example, `as.Date(format(as.Date("01/04/2019", "%m/%d/%Y"),"%Y-%W-1"),"%Y-%W-%u")` returns `NA` because `format(as.Date("01/04/2019", "%m/%d/%Y"),"%Y-%W-1")` returns `"2019-00-1"`. – Rookatu Nov 22 '19 at 23:24

How to get week starting date from a date in R

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