I'm sorry I don't have the exact answer to this, but I can give a few more snippets from my example from above: sample JSON

{"origItems":[{"bundleProduct":"abc","someotherfield":"def"},{"bundleProduct":"xyz","someotherfield":"pqr"}],"someheaderfield":"S"}

so we're looping through the origItems list (alias is itemList), so the code to pull a field is simply:

${itemList.bundleProduct}

You can also do

<#assign arrayOfObjects = m["origItems"]>

then in the loop you can get your index

<#assign prevIter = itemList_index -1>
<#assign currIter = itemList_index>
<#assign nextIter = itemList_index +1>

Then from this, you can test adjacent records

<#if itemList.partition != arrayOfObjects[prevIter].partition>

I think this last example might be useful to you?