If you have two columns of data, what's the easiest way to automatically
(programatically?) interleave them. The resulting column should consist of:

1st cell of 1st column
1st cell of 2nd column
2nd cell of 1st column
2nd cell of 2nd column
etc.

For example,
1 a
2 b
3 c

would become:

1
a
2
b
3
c