Node: maphash, Next: , Previous: remhash, Up: Hash Tables Dictionary



maphash [Function]

maphash function hash-table => nil

Arguments and Values::

function--a designator for a function of two arguments, the key and the value.

hash-table--a hash table.

Description::

Iterates over all entries in the hash-table. For each entry, the function is called with two arguments-the key and the value of that entry.

The consequences are unspecified if any attempt is made to add or remove an entry from the hash-table while a maphash is in progress, with two exceptions: the function can use can use setf of gethash to change the value part of the entry currently being processed, or it can use remhash to remove that entry.

Examples::

      (setq table (make-hash-table)) =>  #<HASH-TABLE EQL 0/120 32304110>
      (dotimes (i 10) (setf (gethash i table) i)) =>  NIL
      (let ((sum-of-squares 0))
         (maphash #'(lambda (key val)
                      (let ((square (* val val)))
                        (incf sum-of-squares square)
                        (setf (gethash key table) square)))
                  table)
         sum-of-squares) =>  285
      (hash-table-count table) =>  10
      (maphash #'(lambda (key val)
                    (when (oddp val) (remhash key table)))
                table) =>  NIL
      (hash-table-count table) =>  5
      (maphash #'(lambda (k v) (print (list k v))) table)
     (0 0)
     (8 64)
     (2 4)
     (6 36)
     (4 16)
     =>  NIL
     

Side Effects::

None, other than any which might be done by the function.

See Also::

loop , with-hash-table-iterator , Traversal Rules and Side Effects