Sure thing. Our mavg functions work for things already in data (securities), but in this case I think you'll need to do it a little differently. The easiest way seems to be using history like this
prices = history(bar_count=20, frequency='1d', field='price')
ratioMA = (prices[sid(x)] / prices[sid(y)]).mean()
Calling history like this will give you a data structure containing the last 20 bars of price data for each security at a daily frequency. You can then index into prices like you did into data to get the 20 bars for that security. Dividing the two and taking the mean will give you the average for the last 20 days. This will be a moving average in your algorithm as the last 20 bars will be updated each time handle_data is called. Is this what you wanted? Another common use case would be computing the moving average for each of the last n days, which would be slightly different.
The material on this website is provided for informational purposes only and does not constitute an offer to sell, a solicitation to buy, or a recommendation or endorsement for any security or strategy, nor does it constitute an offer to provide investment advisory services by Quantopian. In addition, the material offers no opinion with respect to the suitability of any security or specific investment. No information contained herein should be regarded as a suggestion to engage in or refrain from any investment-related course of action as none of Quantopian nor any of its affiliates is undertaking to provide investment advice, act as an adviser to any plan or entity subject to the Employee Retirement Income Security Act of 1974, as amended, individual retirement account or individual retirement annuity, or give advice in a fiduciary capacity with respect to the materials presented herein. If you are an individual retirement or other investor, contact your financial advisor or other fiduciary unrelated to Quantopian about whether any given investment idea, strategy, product or service described herein may be appropriate for your circumstances. All investments involve risk, including loss of principal. Quantopian makes no guarantees as to the accuracy or completeness of the views expressed in the website. The views are subject to change, and may have become unreliable for various reasons, including changes in market conditions or economic circumstances.