# [R] having problems re-ordering a dataframe

Chabot Denis chabotd at globetrotter.net
Sat Oct 27 17:34:14 CEST 2007

```Dear R users,

I need to reorder a dataframe using 3 variables for the determine the
sorting order.

When I create a simple dataframe to test the method, things work as I
expected:

a1 <- rep(1:10, each=8)
a2 <- rep(rep(1:2, each=4), 10)
a3 <- rep(c(1:4),20)
(a <- data.frame(a1, a2, a3))

for each combination of a1 and a2, a3 is increasing

t <- order(a\$a1, a\$a2, rev(a\$a3))
b <- a[t,]

In this new dataframe, the 3rd variable is in decreasing order within
each combination of a1 and a2, which is the desired result.
As expected, this still works if the second variable never changes:

e1 <- rep(1:10, each=8)
e2 <- rep(2, 80)
e3 <- rep(c(1:8),10)
e <- data.frame(e1, e2, e3)
t <- order(e\$e1, e\$e2, rev(e\$e3))
f <- e[t,]

With my real data, I do not get the 3rd variable in inverse order for
each combination of the first 2. Here I recreate the beginning of my
dataframe for you to see what I mean:

c1 <- c(rep(813,102), rep(826,48))
c2 <- rep(2,150)
c3 <- c(seq(1:102), seq(1,48))
c <- data.frame(c1, c2, c3)
t <- order(c\$c1, c\$c2, rev(c\$c3))
d <- c[t,]

The dataframe d is properly ordered for c1==826, but not for c1==813,
where c3 goes from 48 down to 1, and then from 102 down to 49,
instead of going from 102 down to 1. All the variables are numeric,
not factors.

Any help/explanation will be greatly appreciated.

Denis
sessionInfo()
R version 2.6.0 (2007-10-03)
powerpc-apple-darwin8.10.1

locale:
fr_CA.UTF-8/fr_CA.UTF-8/fr_CA.UTF-8/C/fr_CA.UTF-8/fr_CA.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

```