I have the following data frame about registered vehicles in Switzerland:

```
Fuel     Year   Region   Count
Gasoline 2013       GE  169600
Diesel   2013       GE   46790
Hybrid   2013       GE    2268
Electric 2013       GE      85
Other    2013       GE     532
Gasoline 2013       VS  149232
Diesel   2013       VS   50591
Hybrid   2013       VS    1028
Electric 2013       VS     268
Other    2013       VS     261

```

I would like to add an additional "Pct" column in the data frame with the percentage of the fuel type by year and region but I have some difficulties to understand how. The result should be:

```
Fuel     Year   Region   Count  Pct
Gasoline 2013       GE  169600  0.7734
Diesel   2013       GE   46790  0.2134
Hybrid   2013       GE    2268  0.0134
Electric 2013       GE      85  0.0004
Other    2013       GE     532  0.0024
Gasoline 2013       VS  149232  0.7410
Diesel   2013       VS   50591  0.2512
Hybrid   2013       VS    1028  0.0051
Electric 2013       VS     268  0.0013
Other    2013       VS     261  0.0013

```