Hi, there,

I have a simple data manipulation question for you. Thank you for your help!

 Suppose that I have this data about people appearing in a class


Mary
Mary
Mary
Sam
Sam
John
John
John
John

Then I want to find out what exact time(s) the student appears at the
moment such as

 Mary 1
Mary 2
Mary 3
Sam 1
Sam 2
John 1
John 2
John 3
John 4

the fifth row shows tha Sam show the second times at the that moment.

How can I manipulate the data in this way. Suppose that now I just have
"name" variable and want to add a colume of frequency?

Best

Jie

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