Count non-repeated words in cell

[mxc668]

Hi,

I want to count the nr of words in cell without counting the repeated words.
For example, in "this is a ball and that is a square", the total nr of words is 9, and the total nr of non-repeated words is 7, because "is" and "a" are repeated twice, and I just want to count it once.

Please help!

Thanks,
mxc668