title: ipysheet and dataframe. How modify value in a ipysheet when a checkbox is checked
body: <p>Need your help.
  I create a dataframe and load it as ipysheet.
  I overload the column &quot;1&quot; with checkbox.
  Purpose: When I click on a checkbox of a cell of the column 1, I multiplicate the corresponding value in the column &quot;2&quot; by two. (not all the column 2)</p>
  <p>I tried different things but it doesn't work as expected.
  cf code below</p>
  <ul>
  <li><p>So first how to get the value from the ipysheet of the column &quot;2&quot;.
  Something like that but I don't want to overload the datas. i just want to get the existing values.
  <code>#column2 = ipysheet.column(1,[x for x in range(2)])</code></p>
  </li>
  <li><p>How to change a value of an element in the second column when I check something in the first column ?</p>
  </li>
  </ul>
  <p>Thanks for your help,</p>
  <h1>Code to reproduce:</h1>
  <pre><code>import numpy as np
  from ipywidgets import Checkbox
  import pandas as pd
  import ipysheet
  df = pd.DataFrame(np.array([[1, 2], [4, 5]]))
  
  wsMultiple = ipysheet.sheet(ipysheet.from_dataframe(df))
  column1 = ipysheet.column(0,[Checkbox() for _ in range(2)])
  #column2 =  ?
  
  def test(change):
  print(&quot;test&quot;)
  #something like:
  #column2.value = column2.value * 2
  
  column1.observe(test, &quot;value&quot;)
  wsMultiple`
  </code></pre>
  <p><strong>Before:</strong></p>
  <blockquote>
  <p>0          1
  0  checkbox   2
  1  checkbox   5</p>
  </blockquote>
  <p><strong>After</strong> the click on the second checkbox:</p>
  <blockquote>
  <p>0          1
  0  checkbox   2
  1  checkbox   10</p>
  </blockquote>