In Jekyll need to pass reference to a site data set in front matter – but not as string, but with variable contents

This gives me two very different answers, on the variable of interest, “toc”:

Liquid Code to fetch right menu, based on front matter variable page.series

{% for item in site.data.tree-menus.tree %}
 {% if item.name == page.series %} 
   {% assign menu_type = item.link %}
 {% endif %}
{% endfor %}

Using Capture

{% capture toc %}{{menu_type}}{% endcapture %}
{{toc}}

Here toc returns the string:

site.data.tree-menu-1.tree

Note

site.data.tree-menus.tree is reference to a YAML file called tree-menus.yml that looks like the below. It is a reference to other YAML files which contain different menu navigations, e.g. Menu 1, Menu 2 (as I need to show a different side menu, depending on what page is loaded – refer to the top most liquid code snippet):

tree:
- name: Menu 1
  link: site.data.tree-menu-1.tree
- name: Menu 2
  link: site.data.tree-menu-2.tree

Using Assign

{% assign toc = site.data.tree-menu-1.tree %}

{{toc}}

Here toc returns the the contents of this yaml file, called “tree-menu-1.yml”:

tree:
- name: Level 1
  link: /docs/guides/level1.html
- name: 1. Level 2
  link: /docs/level2.html
- name: 2. Level 3
  link: /docs/level3.html

In the final bit of the code, I then pass in toc, to an include, which takes the content of the variable, to generate the Menu (in HTML)

Passing ToC variable into an include

{% include lhsTree.html nav=toc %}

PROBLEM

The problem is, the menu only generates using the assign method, and not the capture method.
For example if I do this,

{% assign toc = {{menu_type}} %}
{{toc}}
{% include lhsTree.html nav=toc %}

Toc will just be a string, it won’t hold the contents of Menu 1, (and the include will generate nothing. But the include is very happy when I do this

{% assign toc = site.data.tree-menu-1.tree %}
{{toc}}
{% include lhsTree.html nav=toc %}

How can I dynamically generate the correct menu, depending on what page is loaded, as I tried to do using the capture method above?

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Author: Sachin