Product variant association

Question

On my Products details page I have 2 selects. The 1st select list out the Primary variants. Based on the selected Primary variant the 2nd select is auto-completed in with Secondary variants that have the same Primary variant.

I am doing setting this initially via an array:

{% set myVariants = [] %}

{% for variant in product.variants %}

{% set variantId = variant.id %}
{% set Primary = variant.primary %}
{% set Secondary = variant.secondary %}

{% if Primary not in myVariants | keys %}
    {% set myVariants = myVariants | merge({
        (Primary): [Secondary]
    }) %}
{% else %}
    {% set myVariants = myVariants | merge({
        (Primary): myVariants[Primary] | merge([Secondary])
    }) %}
{% endif %}

{% endfor %}

This outputs an array like so when dumped:

array(5) { 
  ["0.375"]=> array(2) { 
    [0]=> string(5) "0.125" 
    [1]=> string(5) "0.415" 
  } 
  ["0.500"]=> array(1) { 
    [0]=> string(5) "0.768" 
  } 
  ["0.625"]=> array(1) { 
    [0]=> string(5) "1.151" 
  } 
}

So based on the selected Primary and Secondary variants a specific variant ID should be pulled.

I've tried starting with the variant IDs, then passing the Primary variant to reproduce a similar array like above but it doesn't put them in a 2nd array.

What am I missing?

Also, based on the selection of Primary and Secondary, not only will the ID need to be pulled but also 2 additional variants and the sku; each of which are specific to that variant.