I still don't quite understand the usage of summarize and group_by.Can you interpret the function of summarize and group_by through the following two examples (https://i.stack.imgur.com/A2NDi.png)
[I still don't quite understand the usage of summarize and group_by.Can you interpret the function of summarize and group_by through the two examples？(https://i.stack.imgur.com/qzLrc.png)