TITLE: Dynamic lists from user-added choices within repeats and 
groups, in ODK
DATE: 2021-02-15
AUTHOR: John L. Godlee
====================================================================


For the tree data collection form I have been creating in ODK with 
XLSForm, I wanted to allow users to quickly re-use species names 
from previous species identified within the plot to cut down on 
typing. It stands to reason that if a species is encountered within 
a plot, there are likely other trees of the same species within the 
plot. My mental model for the ODK form was to present the user with 
a repeating question, one iteration for each individual, which 
said: "from the choices listed below, choose the species of tree", 
where the list of choices was populated by answers given by the 
user during previous iterations. If the list didn't contain the 
correct species the user could enter it manually in a question 
below and the name would be added to the list of choices for future 
iterations of the repeat. Currently XLSForm+pyxform lack a method 
to accomplish this, so I posted a reply to a similar question on 
the ODK support forums. I got an incredibly helpful response from a 
member of the core developer team which involved editing the raw 
.xml after the form had been converted. Here is a rundown of the 
method posted using an example where users are asked to record the 
names of animals encountered. First, the .xls file, approximated 
using a markdown table:

  [similar question on the ODK support forums]: 
https://forum.getodk.org/t/generate-multiple-choice-alternatives-bas
ed-on-the-answers-in-a-repeat/10269/16

  type                        name            label                 
                                    choice_filter                   
                       required   appearance     relevance          
     calculation
  --------------------------- --------------- 
--------------------------------------------------------- 
------------------------------------------------------ ---------- 
-------------- ----------------------- -----------------
  begin_repeat                pet             Pet                   
                                                                    
                                                                    
     
  begin_group                 pet_group       Pet                   
                                                                    
                                  field-list                        
     
  calculate                   pos                                   
                                                                    
                                                                    
     position(../..)
  select_one ${animal_type}   animal_select   Select the animal 
type. If not in the list, type below.   position() != 
current()/../pos and animal_type != ''              autocomplete    
                       
  text                        animal_type     Animal type           
                                                                    
                       yes                       ${animal_select} = 
''   
  end_group                   pet_group                             
                                                                    
                                                                    
     
  end_repeat                  pet                                   
                                                                    
                                                                    
     

Technically this file is invalid in its specification. It can be 
awkward to produce XForm .xml from an invalid .xls. I used 
xls2xform from pyxform:

    xls2xform --pretty_print --skip_validate pets.xls pets.xml

pretty_print creates un-minified .xml that is easier to edit, 
--skip_validate allows the .xml file to be produced, where 
otherwise it would be discarded.

After the XML is created it is necessary to edit it. These are the 
offending lines:

    <itemset nodeset="..[position() != ./pos and animal_type != 
'']">
    <value ref="animal_type"/>
    <label ref="animal_type"/>
    </itemset>

Which must be amended to:

    <itemset nodeset="/data/pet[position() != current()/../pos and 
pet_group/animal_type != '']">
        <value ref="pet_group/animal_type"/>
        <label ref="pet_group/animal_type"/>
    </itemset>

This update basically changes the references to take into account 
the nested grouping within the repeat, and changes where the pos 
item updates from.