Another way to do this is to use the xtfrm() function. That function
creates numerical values from many different starting types, so you can
just change the sign to change the sort order:
df[order(df$ID, -xtfrm(df$date2)),]
I never did figure out where the name came from.
Duncan Murdoch
On 21/09/2020 3:41 p.m., Sarah Goslee wrote:
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$date2, decreasing=c(FALSE, TRUE), method="radix"),]
ID date2
2 A1 2005-01-27
1 A1 2004-09-17
3 A1 2003-05-07
4 A2 2017-05-21
5 A2 2016-09-12
6 A3 2013-01-25
7 A4 2019-09-27
Sarah
On Mon, Sep 21, 2020 at 2:41 PM Val <valkr...@gmail.com> wrote:
Hi All,
I am trying to sort dates within a group. My sample data is
df <-read.table(text="ID date
A1 09/17/04
A1 01/27/05
A1 05/07/03
A2 05/21/17
A2 09/12/16
A3 01/25/13
A4 09/27/19",header=TRUE,stringsAsFactors=F)
df$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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