FreeMarker/NetSuite PDF Template - Double sorting by date, with possible empty values

I need to sort a list of records and render them in a table, but they have to be sorted by a "From Date" column, and then by "To Date" at a second level. I checked the documentation for ?sort_by but it doesn't mention any support for double sorting.

Thought these would work but it's doing a different thing.

<#list invoices?sort_by(['from_date', 'to_date']) as inv>

<#list invoices?sort_by("from_date")?sort_by("to_date") as inv>

Also, some records have empty values for "From Date" or "To Date".

EDIT: Adapted code based on the answer by bknights, adding entries with empty values at the end of the table. See his answer for a deeper explanation:

<table>

  <tr>
    <th>name</th>
    <th>quantity</th>
    <th>dateFrom</th>
    <th>dateTo</th>
  </tr>

  <!-- Print entries with from/to dates -->
  <#list records?filter(x -> x.custcol_from_date?has_content && x.custcol_to_date?has_content)?sort_by("custcol_to_date")?sort_by("custcol_from_date") as record>
    <tr>
      <td>${record.name}</td>
      <td>${record.quantity}</td>
      <td>${record.custcol_from_date}</td>
      <td>${record.custcol_to_date}</td>
    </tr>
  </#list>

  <!-- Print entries without from/to date at the end of table -->
  <#list records?filter(x -> !x.custcol_from_date?has_content || !x.custcol_to_date?has_content) as record>
   <tr>
      <td>${record.name}</td>
      <td>${record.quantity}</td>
      <td>${record.custcol_from_date}</td>
      <td>${record.custcol_to_date}</td>
    </tr>
  </#list>

</table>

https://try.freemarker.apache.org/

Data Model:

records=[ { "name": "One", "quantity": "10", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-06-01" }, { "name": "Two", "quantity": "20", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-06-15" }, { "name": "Three", "quantity": "30", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-06-01" }, { "name": "Four", "quantity": "40", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-07-02" }, { "name": "Five", "quantity": "50", "custcol_from_date": "2024-04-01", "custcol_to_date": "2024-06-01" }, { "name": "Six", "quantity": "60", "custcol_from_date": "2024-04-02", "custcol_to_date": "2024-05-10" }, { "name": "Seven", "quantity": "70", "custcol_from_date": "2024-05-01", "custcol_to_date": "" }, { "name": "Eight", "quantity": "80", "custcol_from_date": "2024-04-01", "custcol_to_date": "2024-05-13" }, { "name": "Nine", "quantity": "90", "custcol_from_date": "", "custcol_to_date": "2024-06-01" }, { "name": "Ten", "quantity": "100", "custcol_from_date": "", "custcol_to_date": "" } ]

Old answer:

An adaptation of my Freemarker code:

<table>

  <tr>
    <th>name</th>
    <th>quantity</th>
    <th>dateFrom</th>
    <th>dateTo</th>
  </tr>

  <#assign fromDates = "" />

  <!-- Sort records by from_date, then to_date -->
  <#list records?filter(x -> x.custcol_from_date?has_content && x.custcol_to_date?has_content)?sort_by("custcol_from_date") as record>
    <#assign currentFrom = record.custcol_from_date />

    <#if !(fromDates?has_content)>
      <#assign prevFrom = currentFrom />
      <#assign fromDates = currentFrom + "---" />
    </#if>
    <#if prevFrom != currentFrom>
      <#assign fromDates = fromDates + currentFrom + "---" />
    </#if>
    <#assign prevFrom = currentFrom />
  </#list>

  <#list fromDates?split("---") as fromDate>
    <#if fromDate?has_content>
      <#assign parsedDate = fromDate?date />
      <#list records?filter(x -> x.custcol_from_date?has_content && x.custcol_to_date?has_content && x.custcol_from_date = parsedDate)?sort_by("custcol_to_date") as record>
          <tr>
            <td>${record.name}</td>
            <td>${record.quantity}</td>
            <td>${record.custcol_from_date}</td>
            <td>${record.custcol_to_date}</td>
          </tr>
      </#list>
    </#if>
  </#list>

  <!-- Print entries without from/to date at the end of table -->
  <#list records?filter(x -> !x.custcol_from_date?has_content || !x.custcol_to_date?has_content) as record>
    <tr>
      <td>${record.name}</td>
      <td>${record.quantity}</td>
      <td>${record.custcol_from_date}</td>
      <td>${record.custcol_to_date}</td>
    </tr>
  </#list>

</table>

Can be tested in https://try.freemarker.apache.org/ changing this line:

<#assign parsedDate = fromDate?date />

to

<#assign parsedDate = fromDate />

Data Model:

records=[ { "name": "One", "quantity": "10", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-06-01" }, { "name": "Two", "quantity": "20", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-06-15" }, { "name": "Three", "quantity": "30", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-06-01" }, { "name": "Four", "quantity": "40", "custcol_from_date": "2024-05-31", "custcol_to_date": "2024-07-02" }, { "name": "Five", "quantity": "50", "custcol_from_date": "2024-04-01", "custcol_to_date": "2024-06-01" }, { "name": "Six", "quantity": "60", "custcol_from_date": "2024-04-02", "custcol_to_date": "2024-05-10" }, { "name": "Seven", "quantity": "70", "custcol_from_date": "2024-05-01", "custcol_to_date": "" }, { "name": "Eight", "quantity": "80", "custcol_from_date": "2024-04-01", "custcol_to_date": "2024-05-13" }, { "name": "Nine", "quantity": "90", "custcol_from_date": "", "custcol_to_date": "2024-06-01" }, { "name": "Ten", "quantity": "100", "custcol_from_date": "", "custcol_to_date": "" } ]

Result: