I have a file which is sorted using sort -n. However, in order to make a surface plot in gnuplot, I need there to be a blank line between lines with differing values of the first column. for example 

```
1.0
1.0
1.1
1.1

```

to:

```
1.0
1.0

1.1
1.1

```

is there any way to do this easily with Ubuntu Linux?