是否有任何类似于 itertools.groupby()
的 C++ 转换? ?
当然,我可以轻松编写自己的代码,但我更喜欢利用惯用行为,或者根据 STL 或 boost
提供的功能编写一个。
#include <cstdlib>
#include <map>
#include <algorithm>
#include <string>
#include <vector>
struct foo
{
int x;
std::string y;
float z;
};
bool lt_by_x(const foo &a, const foo &b)
{
return a.x < b.x;
}
void list_by_x(const std::vector<foo> &foos, std::map<int, std::vector<foo> > &foos_by_x)
{
/* ideas..? */
}
int main(int argc, const char *argv[])
{
std::vector<foo> foos;
std::map<int, std::vector<foo> > foos_by_x;
std::vector<foo> sorted_foos;
std::sort(foos.begin(), foos.end(), lt_by_x);
list_by_x(sorted_foos, foos_by_x);
return EXIT_SUCCESS;
}
最佳答案
这并不能真正回答您的问题,但为了好玩,我实现了一个 group_by 迭代器。也许有人会觉得它有用:
#include <assert.h>
#include <iostream>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using std::cout;
using std::cerr;
using std::multiset;
using std::ostringstream;
using std::pair;
using std::vector;
struct Foo
{
int x;
std::string y;
float z;
};
struct FooX {
typedef int value_type;
value_type operator()(const Foo &f) const { return f.x; }
};
template <typename Iterator,typename KeyFunc>
struct GroupBy {
typedef typename KeyFunc::value_type KeyValue;
struct Range {
Range(Iterator begin,Iterator end)
: iter_pair(begin,end)
{
}
Iterator begin() const { return iter_pair.first; }
Iterator end() const { return iter_pair.second; }
private:
pair<Iterator,Iterator> iter_pair;
};
struct Group {
KeyValue value;
Range range;
Group(KeyValue value,Range range)
: value(value), range(range)
{
}
};
struct GroupIterator {
typedef Group value_type;
GroupIterator(Iterator iter,Iterator end,KeyFunc key_func)
: range_begin(iter), range_end(iter), end(end), key_func(key_func)
{
advance_range_end();
}
bool operator==(const GroupIterator &that) const
{
return range_begin==that.range_begin;
}
bool operator!=(const GroupIterator &that) const
{
return !(*this==that);
}
GroupIterator operator++()
{
range_begin = range_end;
advance_range_end();
return *this;
}
value_type operator*() const
{
return value_type(key_func(*range_begin),Range(range_begin,range_end));
}
private:
void advance_range_end()
{
if (range_end!=end) {
typename KeyFunc::value_type value = key_func(*range_end++);
while (range_end!=end && key_func(*range_end)==value) {
++range_end;
}
}
}
Iterator range_begin;
Iterator range_end;
Iterator end;
KeyFunc key_func;
};
GroupBy(Iterator begin_iter,Iterator end_iter,KeyFunc key_func)
: begin_iter(begin_iter),
end_iter(end_iter),
key_func(key_func)
{
}
GroupIterator begin() { return GroupIterator(begin_iter,end_iter,key_func); }
GroupIterator end() { return GroupIterator(end_iter,end_iter,key_func); }
private:
Iterator begin_iter;
Iterator end_iter;
KeyFunc key_func;
};
template <typename Iterator,typename KeyFunc>
inline GroupBy<Iterator,KeyFunc>
group_by(
Iterator begin,
Iterator end,
const KeyFunc &key_func = KeyFunc()
)
{
return GroupBy<Iterator,KeyFunc>(begin,end,key_func);
}
static void test()
{
vector<Foo> foos;
foos.push_back({5,"bill",2.1});
foos.push_back({5,"rick",3.7});
foos.push_back({3,"tom",2.5});
foos.push_back({7,"joe",3.4});
foos.push_back({5,"bob",7.2});
ostringstream out;
for (auto group : group_by(foos.begin(),foos.end(),FooX())) {
out << group.value << ":";
for (auto elem : group.range) {
out << " " << elem.y;
}
out << "\n";
}
assert(out.str()==
"5: bill rick\n"
"3: tom\n"
"7: joe\n"
"5: bob\n"
);
}
int main(int argc,char **argv)
{
test();
return 0;
}
关于像python的 'groupby'这样的C++算法,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/12335860/