Question: After being a MATLAB user for many years, I am now migrating to python.

I try to find a concise manner to simply rewrite the following MATLAB code in python:

```
s = sum(Mtx);
newMtx = Mtx(:, s>0);

```

where Mtx is a 2D sparse matrix

My python solution is:

```
s = Mtx.sum(0)
newMtx = Mtx[:, np.where((s>0).flat)[0]] # taking the columns with nonzero indices

```

where Mtx is a 2D CSC sparse matrix

The python code is not as readable / elegant as in matlab.. any idea how to write it more elegantly?

Thanks!

Answer: 
There are several ways to solve this, but since I was looking for a fix to Bjarne's code in the presentation slides, I'm accepting this answer which @robson3.14 left in comments to the question:

```
#include <iostream>

template<int M, int K, int S> struct Unit { // a unit in the MKS system
    enum { m=M, kg=K, s=S };
};

template<typename Unit> // a magnitude with a unit
struct Value {
    double val; // the magnitude
    // construct a Value from a double
    constexpr explicit Value(double d) : val(d) {} 
};

using Meter = Unit<1,0,0>; // unit: meter
using Second = Unit<0,0,1>; // unit: sec
using Speed = Value<Unit<1,0,-1>>; // meters/second type

// a f-p literal suffixed by ‘_s’
constexpr Value<Second> operator "" _s(long double d)
{
    return Value<Second> (d);
}
// a f-p literal suffixed by ‘_m’
constexpr Value<Meter> operator "" _m(long double d)
{
    return Value<Meter> (d);
}
// an integral literal suffixed by ‘_m’
constexpr Value<Meter> operator "" _m(unsigned long long d)
{
    return Value<Meter> (d);
}

template<int m1, int k1, int s1, int m2, int k2, int s2>
Value<Unit<m1 - m2, k1 - k2, s1 - s2>> operator / (Value<Unit<m1, k1, s1>> a, Value<Unit<m2, k2, s2>> b)
{
    return Value<Unit<m1 - m2, k1 - k2, s1 - s2>>(a.val / b.val);
}

int main()
{
    Speed sp1 = 100_m / 9.8_s;
    std::cout << sp1.val;
}

```
Not sure this is what you want, it is ugly, but it works :)
You can wrap the type into a template class,

```
template <typename T, int N> // N is used for tagging
struct strong_typedef
{
    using strong_type = strong_typedef<T,N>; // typedef for the strong type
    using type = T; // the wrapped type
    T value; // the  wrapped value

    strong_typedef(T val): value(val){}; // constructor
    strong_typedef(){value={};}; // default, zero-initialization

    // operator overloading, basic example: 
    strong_type operator+(const strong_type& rhs) const
    {
        return value + rhs.value;
    }

    // display it
    friend ostream& operator<<(ostream & lhs, const strong_typedef& rhs)
    {
        lhs << rhs.value;
        return lhs;
    }
};

```

then use it as

```
// these are all different types
strong_typedef<double, 0> x = 1.1; 
strong_typedef<double, 1> y = 2.2;
strong_typedef<double, 2> z = 3.3;

std::cout << x + x << std::endl; // outputs 2.2, can add x and x
// cout << x + y << endl; // compile-time ERROR, different types

```

`x`, `y` and `z` are 3 different types now, because of the different `N`-s used in the template. You can access the type and value using the fields `type` and `value`, like `x::value` (will be double 1.1). Of course if you directly `typedef` the `struct_typedef::type`, you're back to square one, as you are losing the `strong` type. So basically your type should be `strong_typedef` and not `strong_typedef::type`.