Assume a dataframe constructed like

```
df = data.frame(replicate(2,sample(0:10,2,rep=TRUE)))
df = t(df)
df
```

which returns something like

```
[,1] [,2]
X1 9 8
X2 10 4
```

Here's the question: How can I change the order of rows so that:

```
[,1] [,2]
X2 10 4
X1 9 8
```

? Thanks!