title: how to shift value in dataframe using pandas?
body: <p>I have data like this, without z1, what i need is to add a column to DataFrame, so it will add column z1 and represent values as in the example, what it should do is to shift z value equally on 1 day before for the same Start date.  </p>
  
  <p><a href="https://i.stack.imgur.com/DUqvI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DUqvI.png" alt="enter image description here"></a>
  I was thinking it could be done with apply and lambda in pandas, but i`m not sure how to define lambda function</p>
  
  <pre><code>data = pd.read_csv("....")
  
  data["Z"] = data[[
                  "Start", "Z"]].apply(lambda x:
  </code></pre>