I have the Daily market value data of listed companies，like:
stock_code date ME
1 01oct1978 1000000
1 02oct1978 1100000
...
1 31oct1978 1500000
1 01nov1978 1600000
...
1 30jul2019 5000000
2 01oct1978 2000000
2 02oct1978 2100000
...
2 31oct1978 2500000
2 01nov1978 2600000
...
2 30jul2019 8000000
now I want to group the market value of listed companies according to a specific date,
Divide into two groups (Small or Big) based on the market capitalization of all listed companies at the end of June(like June 31 or 30).
How can I do this?I know how to divide two groups based on every ME, It's simple. But I can't Group the market value of listed companies according to a specific date.
Plese help me.