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