Axel, The main problem for me, is that I'm obligated to print the computation, that's why I'm looking for a solution to compute and show results on the qweb template, if only there is a way to collect data, compute on the background via a functionnal field, and show computation results via a new qweb report (survey answers), it will be a great solution. What do you think of mi idea ? do you think is technically doable ? 

From my point of view the best way to solve this is by doing the computation in a parser method that return the list of rows to display and iterate that list in the qweb report template. An example for your image

def crosstab(self, values):
    crosstab = []
    headers = ('','Col 1', 'Col 2')
    crosstab.append(headers)
    crosstab.append(('Line 1', 'Value (1,1)', 'Value (1,2)'))
    crosstab.append(('Line 2', 'Value (2,1)', 'Value (2,2)'))
    #calculate the rest of the lines or the previous to add the result to the list
    crosstab.append(('Line 1', 'Value (1,1)', 'Value (1,2)'))

    return crosstab

Use like this in the qweb report template:

<table class="table table-bordered">
  <t t-foreach="crosstab(value)" t-as="row">
    <tr>
      <t t-foreach="row" t-as="measure">
        <td t-esc="measure"/>
      </t>
    </tr>
  </t>
</table>

Change value to what you need to pass to the report function as an argument or pass more or less arguments depending of what you need to use to compute the crosstab table measures

Here is how to add functions in the parser, config the parser and use it on the qweb report template:

https://www.odoo.com/es_ES/forum/help-1/question/how-to-define-a-custom-methods-functions-to-be-used-in-a-qweb-report-how-to-define-and-use-a-report-parser-92244