Dividing 8 levels within subject into two variables

[or duek]

Hi,
I have a task which contains 8 blocks. The first four blocks are one condition and the second four blocks are another condition.
How can I divide this within variables into two different ones (block, parts?)
Thank you very much,
Or D.

[Thom]

If I have understood correctly you just need to create two factors that code for this.

e.g., 

block <- gl(4,1,40)

condition <- gl(2,40)

might do it for 40 trials ...