我有一个sqlite3数据库，我需要从中获取数据，然后以编程方式计算每个id的数据量。我不应该使用数据库查询。
答案 0 :(得分：0)
您可以使用groupby函数直接将sqlite3表加载到pandas。然后，您可以使用pandas库中的.count()函数按ID分组，然后使用#include <iostream>
#include <vector>
template<typename value_t, typename left_t, typename right_t, typename op_t>
class Expression
{
public:
typedef value_t value_type;
explicit Expression(const left_t &left,
const right_t &right,
const op_t &op) :
left(left),
right(right),
op(op)
{
}
value_t operator [](const size_t &i) const
{
return op(left[i],right[i]);
}
size_t size() const { return left.size();}
private:
const left_t &left;
const right_t &right;
//const left_t left;
//const right_t right;
const op_t &op;
};
template<class left_t,
class right_t,
class value_t = typename left_t::value_type,
class op_t = std::plus<value_t>>
const Expression<value_t, left_t, right_t, op_t> operator +(const left_t &left,
const right_t &right)
{
return Expression<value_t,left_t,right_t,op_t>(left, right, op_t());
}
template<typename value_t, typename data_t = std::vector<value_t>>
class Vector : public data_t
{
public:
typedef value_t value_type;
using data_t::size;
Vector(const std::initializer_list<value_t> &list) :
data_t(list)
{
}
Vector(const size_t &n) :
data_t(n)
{
}
Vector(const Vector &v) :
data_t(v)
{
}
template<typename left_t, typename right_t, typename op_t>
Vector(const Expression<value_t,left_t,right_t,op_t> &v) :
data_t(v.size())
{
operator =(v);
}
template<typename vec_t>
Vector(const vec_t &v) :
data_t(v.size())
{
operator =(v);
}
template<typename vec_t>
Vector &operator =(const vec_t &v)
{
for(size_t i = 0; i < data_t::size(); ++i)
data_t::operator [](i) = v[i];
return (*this);
}
friend std::ostream &operator <<(std::ostream &os, const Vector &v)
{
if(v.size())
os << v[0];
for(size_t i = 1; i < v.size(); ++i)
os << " " << v[i];
return os;
}
};
int main()
{
Vector<double> a{0,1,2};
auto b = a+a+a;
auto c = a;
std::cout << a+a+a+a << std::endl;
std::cout << b+c << std::endl; // gives bad_alloc
return 0;
}
获取每个ID的计数。