Consider a recfile containing a list of items in a shop inventory. For each item it is stored its type, its category, its price, the date of the last selling operation of an item of that type, and the amount of items currently available in stock. A sample of such a database could be:
Type: EC Car
Category: Toy
Price: 12.2
LastSell: 20-April-2012
Available: 623
Type: Terria
Category: Food
Price: 0.60
LastSell: 22-April-2012
Available: 8239
Type: Typex
Category: Office
Price: 1.20
LastSell: 22-April-2012
Available: 10878
Type: Notebook
Category: Office
Price: 1.00
LastSell: 21-April-2012
Available: 77455
Type: Sexy Puzzle
Category: Toy
Price: 6.20
LastSell: 6.20
Available: 12
Now imagine we are interested in grouping the contents of the
Items record set in groups of items of the same category. We
can do it using the -G command line argument for
recsel. This argument accepts a list of fields separated by
commas. The argument can be read as “group by”.
In this case we want to group by Category, so we would do:
$ recsel -G Category
Type: Terria
Category: Food
Price: 0.60
LastSell: 22-April-2012
Available: 8239
Type: Typex
Category: Office
Price: 1.20
LastSell: 22-April-2012
Available: 10878
Type: Notebook
Price: 1.00
LastSell: 21-April-2012
Available: 77455
Type: EC Car
Category: Toy
Price: 12.2
LastSell: 20-April-2012
Available: 623
Type: Sexy Puzzle
Price: 6.20
LastSell: 6.20
Available: 12
We can see that the output is three records, corresponding to the three
different categories of items present in the database.
However, we are only interested in the types of products in each category,
so we can remove unwanted information using -p:
$ recsel -G Category -p Category,Type items.rec
Category: Food
Type: Terria
Category: Office
Type: Typex
Type: Notebook
Category: Toy
Type: EC Car
Type: Sexy Puzzle
It is also possible to group by several fields. We could group by
both Category and LastSell:
$ recsel -G Category,LastSell -p Category,LastSell,Type items.rec
Category: Food
LastSell: 22-April-2012
Type: Terria
Category: Office
LastSell: 21-April-2012
Type: Notebook
Category: Office
LastSell: 22-April-2012
Type: Typex
Category: Toy
LastSell: 20-April-2012
Type: EC Car
Category: Toy
LastSell: 6.20
Type: Sexy Puzzle