title: How to undo a command in jupyter notebook after execution a No. of command?
body: <ol>
  <li>How i can undo a command in jupyter notebook, let suppose in the provided code i treated outliers in my <code>data['age']</code> column by replacing them by a value 72 for all the outliers which lies beyond 72 (as shown in the below code). But after few more finding i thought it would be appropriate if i replace values which is beyond 75 not 72 in 'age' column. how can i retrieve my data back as i have already ran few more commands after this line?</li>
  <li>if accidentally i deleted a column in my data and saved it as in the same variable data(as shown in below code for column 'customer ID'), then how can i get it back? as i have already ran many commands after deleting the column.</li>
  </ol>
  
  <pre><code>#1
  data[(data['age']&gt;72)]==72
  </code></pre>
  
  <pre><code>#2
  data=data.drop(columns='customer ID',axis=1)
  </code></pre>