Proposed algorithm library: reduce, combine, filter, guard

From: farrow_at_[hidden]
Date: 2001-08-09 14:22:39

Using STL algorithms...
I am unable to deduce a way of combining or reducing sequence
containers into a single result or filtering arbitrary iterators with
a predicate.  So I have created these...

REDUCE: applies a binary operator where the first argument is the
current intermediate result and the second is each value in the
sequence.  The result of each function application becomes the new
result.

Example:

vector<int> nums; //contains { 1, 2, 3 }
int result = reduce(nums.begin(), nums.end(), plus<int>(), 0);
//result = 6

COMBINE: applies the plus operator to the elements in a sequence with
a separator.  Mostly useful for containers of strings -- but not
limited to that.

Example:

string sep("|");
vector<string> strs; //contains { "a", "b", "c" }
string result = combine(strs.begin(), strs.end(), sep)
//result = "a|b|c"

FILTER: a wrapper for an iterator that applies a predicate functor.
The resulting iterator only stops at objects that pass the predicate.

vector<int> nums; //contains { 1, 15, 2, 10, 3 }
int result = reduce(filter(nums.begin(),
                           bind2nd(less_than<int>(),10)),
                    nums.end(), plus<int>(), 0);
//result = 6

GUARD: is the complement of FILTER.
The resulting iterator only stops at objects that FAIL the predicate.

I have not found these (or the like) in STL or after looking thru
several on-line repositories -- Boost and others recommended by
"Effective STL" (by Meyers).

I don't contend that these interfaces are perfect and 
I am happy to be refered to someone else's work.

Thanks,

Rob Farrow
farrow_at_[hidden]