9.30 GeneralSparseTable

Sometimes when working with tables there is a natural value to use as the entry in all but a few cases. The GeneralSparseTable constructor can be used to provide any table type with a default value for entries. See TableXmpPage for general information about tables.

Suppose we launched a fund-raising campaign to raise fifty thousand dollars. To record the contributions, we want a table with strings as keys (for the names) and integer entries (for the amount). In a data base of cash contributions, unless someone has been explicitly entered, it is reasonable to assume they have made a zero dollar contribution.

This creates a keyed access file with default entry 0.

patrons: GeneralSparseTable(String, Integer, KeyedAccessFile(Integer),

0. := table() ;

_{Type: GeneralSparseTable(String,Integer,KeyedAccessFile Integer,0)}

Now patrons can be used just as any other table. Here we record two gifts.

patrons."Smith" := 10500

\[\]

10500

_{Type: PositiveInteger}

patrons."Jones" := 22000

\[\]

22000

_{Type: PositiveInteger}

Now let us look up the size of the contributions from Jones and Stingy.

patrons."Jones"

\[\]

22000

_{Type: PositiveInteger}

patrons."Stingy"

\[\]

0

_{Type: NonNegativeInteger}

Have we met our seventy thousand dollar goal?

reduce(+, entries patrons)

\[\]

32500

_{Type: PositiveInteger}

So the project is cancelled and we can delete the data base:

)system rm -r kaf*.sdata