[USER (data scientist)]: Awesome, that's what I needed. now can you help me find the number of properties in this filtered dataset? Please load the 'melb_data.csv' dataset into a DataFrame and calculate the number of properties in it, storing the result as an integer in a pickle file.
My template of code snippet is:

---BEGIN CODE TEMPLATE---

import matplotlib.pyplot as plt
import pandas as pd
import pickle

melbourne_housing = pd.read_csv("melb_data.csv") 

# YOUR SOLUTION BEGIN:
<code1>
[GENERATE YOUR CODE]
</code1>
# YOUR SOLUTION END:

print(number_of_properties)

# save data
pickle.dump(number_of_properties,open("./pred_result/number_of_properties.pkl","wb"))

---END CODE TEMPLATE---

[YOU (AI assistant)]: Sure thing! You can use this code to count the number of properties in the filtered dataset: 
