Ordering date/time in descending order in R -

i have data frame df 1 of columns being date/time , order data frame in descending order of column.

df <- data.frame(id=c('id3', 'id2','id1'), end=c('4/1/10 12:00', '6/1/11 14:20', '1/1/09 11:10'), age=c(40,30,20)); 

i first converted end column et using et = as.posixct(df$end,format='%m/%d/%y %h:%m'), , used following, got error unary operator '-' not accepted argument :

out <- df[order(-df$et),]; 

i tried used descending flag again got error arguments not being of same length.

out <- df[order(df$et, descending=true),]; 

however, ascending order seems work: out <- df[order(df$et),].

how can order in descending order (most recent time first)? thank you.

i think work:

## bigger dataset 2 times on same day: df <- data.frame(id=c('id3', 'id2','id1','id4'), end=c('4/1/10 12:00', '6/1/11 14:20', '1/1/09 11:10' , '1/1/09 13:11'), age=c(40,30,20,20));  ## note self - include timezone. df$dtime <- as.posixct( df$end , format = "%d/%m/%y %h:%m" , tz = "gmt") df[ order(df$dtime , decreasing = true ),] #   id          end age               dtime #2 id2 6/1/11 14:20  30 2011-01-06 14:20:00 #1 id3 4/1/10 12:00  40 2010-01-04 12:00:00 #4 id4 1/1/09 13:11  20 2009-01-01 13:11:00 #3 id1 1/1/09 11:10  20 2009-01-01 11:10:00