improve this code based on the following, Design a DatasetManager class to handle loading, preprocessing, and transforming the dataset.

import pandas as pd

class DatasetManager:

def $\_\_$init$\_\_($self$,$ url$)$:

self.url $=$ url

self.data $=$ None

def load$\_$data$($self$)$:

self.data $=$ pd$.$read$\_$csv$($self$.$url, sep$=\text{'}$;$\text{'})$

return self.data

def preprocess$\_$data$($self$)$:

self.data.fillna$($method$=$'ffill', inplace$=$True$)$

self.data $=$ pd$.$get$\_$dummies$($self$.$data$)$

return self.data

def get$\_$students$($self$)$:

students $=[]$

for idx, row in self.data.iterrows$()$:

student $=$ Student$($

id$=$row$[\text{'}$ID$\text{'}],$

name$=$row$[\text{'}$Name$\text{'}],$

grades$=[$row$[\text{'}$G$1\text{'}],$ row$[\text{'}$G$2\text{'}],$ row$[\text{'}$G$3\text{'}]]$

$)$

students.append$($student$)$

return students