Help Getting Total Market Cap in Sector

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Help Getting Total Market Cap in Sector

posted Oct 18, 2018

I'm trying to get the total market cap in a sector by day. I'm new to coding in general as you can probably tell. I think I'm on the right track but I can't figure out how to sum the market cap for all stocks in my universe daily. I have tried tech_stocks['market_cap'].sum() but it adds all the days together. Just to be clear because I'm new to this and don't know if I'm explaining it right, I want to end up with one market cap number per trading day that is the sum of my selected stocks market caps. I'm planning on plotting this along with a moving average of the market cap. Also, I have a price filter to limit the selection until I get it working to make the data easier to handle.

Thanks for helping me out.

PS - I'm aware that their are Sector ETF's and such that I could use instead, but at this point I just want to figure out how to do it myself. It's not for any real world trading, just learning.

3 responses

You are looking for the groupby method (https://pandas.pydata.org/pandas-docs/version/0.18/generated/pandas.DataFrame.groupby.html). Something like this

tech_stocks.market_cap.groupby(level=0).sum()

What that does is starts with the 'tech_stock' dataframe. Then selects the 'market_cap' column. Then applies the 'groupby method. The initial dataframe has a multi index (first indexed by date - level 0, and then by security - level 1) . If one wants to group by date then specify 'level=0' . It's often less cryptic to first name the indexes (eg 'date' and 'security') so one could simply group by 'date' for easier reading.

Once the data is grouped, then apply the 'sum' method. There are a number of methods which could also be applied.

See attached notebook. Hope that helps.

Thanks Dan! I also really appreciate you explaining it in detail so that I understand it. That will help me remember it down the road.

@Brett. Always glad to help. Good luck!

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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.