Fortran associative array

A scalable associative array (known as hash table or dictionary) for Fortran

Specifications

• Internal data structure is treap (randomized binary search tree)

• Roughly corresponds to std::map (C++) or dict (Python)

  • A key can be characters (either fixed or arbitrary length), an integer, or a real
  • A value can be any fortran intrinsic data type (with fixed length or kind). A copy of the value is stored in the dict object
  • Does not affect Fortran's intrinsic random state

• Implemented operations

  Operation	Cost	Implementation
  Insertion/assignment	O(log n)	Subroutine insert_or_assign(dict, key, val)
  Deletion	O(log n)	Subroutine remove(dict, key) (Error if not exist)
  Existence of a key	O(log n)	Logical function exists(dict, key)
  Reference	O(log n)	Valuetype function get_val(dict, key) (Error if not exist)
  Get max/min/k-th key	O(log n)	Keytype function get_kth_key(dict, k) (Error if out of bounds; 1-based)
  Count	O(1)	Integer function get_size(dict)
  Retrieve sorted array	O(n)	Subroutine get_keys_vals(dict, keys, vals, n) (Not for arbitrary length keys)
  Clear	O(n)	Implicitly called as a destructor

• Other operations allowed by the data structure (not implemented)

  Operation	Cost	Note
  Merge/split	O(log n)	Destructive
  lower_bound/upper_bound	O(log n)
  Range search	O(log n + elements found)
  Deep copy	O(n)	Preorder DFS

• Speed comparison with gfortran/g++, without compiler optimization

  

Usage

• See sample.f90 for sample usage
• Edit dtypes.h if using another data types
  • For string key (arbitrary length), keytype1 should be character(:),allocatable and keytype2 should be character(*)
  • For other key types, keytype1 and keytype2 are the same

References

• Treap https://en.wikipedia.org/wiki/Treap
• Treap https://www.slideshare.net/iwiwi/2-12188757