Hash Table Functions

makeHashTable

Function

makeHashTable test

Function

makeHashTable test size

Function

makeHashTable returns a new Lpp hash table object. If the optional argument test is given it should be a predicate function object of two arguments that returns nil unless the two arguments representing hash table keys are considered equal by the definition of the function. Or test may be one of the symbols: eq, eql or equal which would correspond to the function of that symbol name. If test is not given or nil it is assumed to be the eql function.

The optional argument size if given should be an positive integer argument specifying the size of the hash table. size may be of type int or Lpp Integer. If size is not given or nil then a default size of approximately 500 is used. The user is encouraged here to either use the default size or study how to compute the optimal size of hash tables (See Knuth "Art of Computer Programming"). Although all sizes will work under Lpp some sizes will result in better distributions.

puthash key table value

Function

puthash creates an entry for key with value value in the hash table table. If the key entry already exists in table then its value is replaced with value. value is returned.

gethash key table

Function

gethash key table default

Function

gethash finds the entry for key in the hash table table and returns the entry value. If not found it returns nil. If the optional third argument default is specified and the key is not found default is returned instead of nil.

Here is an example:

     let table = makeHashTable();
     let max = L(100); let min = L(0);
     puthash(S(red), table, list(max, min, min));
     puthash(S(green), table, list(min, max, min));
     gethash(S(blue), table) => nil
     gethash(S(red), table) => (100 0 0)
     

remhash key table

Function

remhash removes the entry for key in hash table table. This is also a predicate that returns t if there was an entry and nil if not.

clrhash table

Function

clrhash removes all entry from the hash table table and returns table.

hashTableCount table

Function

hashTableCountL table

Function

hashTableCount returns the number of entries in hash table table as an int. hashTableCountL does the same but returns an Lpp Integer. A hash table starts out with zero entries.

maphash function table

Function

For each entry in hash table table maphash calls function function on two arguments: the key of the entry and the value of the entry. For example the following maphash would display the key and value for all entries in hash table ht

     let printKeyValue(let key, let value) {
       princ("  key = "); prin1(key);
       princ("    value = "); prin1(value); terpri();
       return Nil;}
     
     maphash(L(printKeyValue), ht);