A multi-select option to choose to filter available cities.
We'll go through all of this step by step so that you can easily pull our the parts you need into your own application.
Reading our data
Our dataset contains a number of columns. It's already clean, so we don't need to make many changes. We are mainly interested in the "price", "num_rooms" and "city" columns.
Create a file called app.py and add the following code.
```python
import streamlit as st
import pandas as pd
import altair as alt
DATA_SOURCE = "./data/bern_rentals.csv"
@st.cache
def load_data():
    data = pd.read_csv(DATA_SOURCE)
    data['date'] = pd.to_datetime(data['date'])
    data['Size'] = data['size'].apply(lambda x: f'{x:.0f} sqm')
    data['Price'] = data['price'].apply(lambda x: f'CHF {x:.0f}')
    return data
```
