How to ignore NaN values in price2ret

Hi,

Is there any efficient code to get from vector [99;NaN;100;102] the following result:

[NaN;NaN;0.01010101;0.02] using the formula price2ret

it means that for the second day there is no return as there is no price, but for the third day matlab ignores NaN (in the second day) and instead it takes the price form the first day (99).

thanks