Question

I can’t wrap my head around the following Stata programming problem:

I have a table listing all car purchases by customers and make:

Customer | Make | Price
-----------------------
      c1 |   m1 |     1
      c1 |   m1 |     2
      c1 |   m3 |     1
      c2 |   m2 |     2
      c3 |    . |     .

I want to transform this into a table with one observation/row per customer, listing the maximum price paid for every make:

Customer | m1 | m2 | m3
-----------------------
      c1 |  2 |  0 |  1
      c2 |  0 |  1 |  0
      c3 |  0 |  0 |  0

How do I achieve this? I know reshape wide, but that doesn’t work because of the doubled c1 | m1 row. Also, the missing values for c3 are causing troubles.

Answer 1

Depending on what you want to do, I suggest approaching this a little differently. For example using -bysort- you can find the maximum price by customer for each make.

bysort Customer Make : egen maxPrice = max( Price )

Or, you can use collapse to find the max price by customer and make:

collapse (max) Price, by( Customer Make )

But, if you really want the table you posted using -reshape- you could run the following:

collapse (max) Price, by( Customer Make )
drop if Price == .
reshape wide Price, i( Customer ) j( Make ) string
renpfix Price 

Note that reshape will fail if it encounters missing data in the Price column. I dropped these observations in the code above but you may choose to do something different like replace the missing data with zeros as you show in your posted target table.