How to find frequency of string data on repeated cross section using STATA? So I am looking at a dataset for auctions. I have all the bidders who won something, and how much they bid. This auction takes place every year. I wanna see if the same people come back every year to participate in the auction. I thought that maybe doing a histogram to compare frequencies might summarize the data nicely. However, because my data has a time component involved, and I would like to see the frequency for all years, is there any other way to find out if the same individual repeats itself in the data at a later date?
 A: I'm going to make some assumptions about your data based on what you said, but if they are incorrect please respond and I'll try to correct my answer.
It would appear that you have basically three primary variables: purchaser, year and price. I'm sure there are others, but let's concentrate on the three for now. Effectively, what you need to do is create a new dataset which turns the purchaser variable into a unique variable, and changes the year variable into several variables. This will allow you to have the third variable, price, as the value under each year variable. Try reshape wide price, i(purchaser) j(year). You'll have to do a bunch of variable name cleanup afterwards, but it should get your data in the correct format. After that, try using the groups package (you'll have to install it using ssc install groups) and run the help groups command to better get an idea of how to use this very powerful command to display your data, but the basic idea would be groups purchaser year1 year2 year3, missing. 
