[R] date

[Sarah Goslee]

Hi,

Nice reproducible example.

rev(df$date2) isn't doing what you think it's doing - try looking at
it by itself.

Some digging into ?order will get you what you are after:

df[order(df$ID, df$date2, decreasing=c(FALSE, TRUE), method="radix"),]

> df[order(df$ID, df$date2, decreasing=c(FALSE, TRUE), method="radix"),]
  ID      date2
2 A1 2005-01-27
1 A1 2004-09-17
3 A1 2003-05-07
4 A2 2017-05-21
5 A2 2016-09-12
6 A3 2013-01-25
7 A4 2019-09-27

Sarah

On Mon, Sep 21, 2020 at 2:41 PM Val <valkremk using gmail.com> wrote:
>
> Hi All,
>
> I am trying to sort dates within a group. My sample data is
>
> df <-read.table(text="ID date
> A1   09/17/04
> A1   01/27/05
> A1   05/07/03
> A2   05/21/17
> A2   09/12/16
> A3   01/25/13
> A4   09/27/19",header=TRUE,stringsAsFactors=F)
> df$date2 = as.Date(strptime(df$date,format="%m/%d/%y"))
> df$date =NULL
>
> I want to sort  date2  from recent to oldest.  within the ID group and
> I used this,
> df <- df[order(df$ID, rev((df$date2))),]. It did not work and teh
> output is  shown below.
>
> ID      date2
> 2 A1 2005-01-27
> 3 A1 2003-05-07
> 1 A1 2004-09-17
> 5 A2 2016-09-12
> 4 A2 2017-05-21
> 6 A3 2013-01-25
> 7 A4 2019-09-27
> What am I missing?
> Thank you.
>
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-- 
Sarah Goslee (she/her)
http://www.numberwright.com