Comparing two arrays, checking for matching values - arrays

Question

Using HubL (as I'm building a module in HubSpot), I have two arrays:
topics : Which is a list of topics.
all_tags: Which is an array of all the blog tags in the system.
If I dump out these arrays, this is what it will return:
{{ topics }} prints the following: [Data, Accounting, Insight]
{{ all_tags }} prints the following: [Accounting, Press, Data]
So essentially, {{ topics }} has a tag ("Insight") that doesn't exist in the system yet.
What I'm trying to do is to create a third array, which will contain matching results from the two above arrays. For example, topics_final, once returned, should print [Data, Accounting].
But, when printing {{ topics_final }}, the array is empty.
What I've tried:
<!-- this gets all tags -->
{% set all_tags = blog_topics( blog_id , 250) %}
<!-- create arrays -->
{% set topics = [] %}
{% set topics_final = [] %}
<!-- append topic data to the array -->
{% for item in module.add_topics.topics %}
{% set topic_option = item|striptags %}
{% do topics.append( topic_option ) %}
{% endfor %}
<!-- check if topic tags exists in HubSpot -->
{% for topics in all_tags %}
{% if topics in all_tags %}
{{ topics }}
<!-- results with above
Data, Accounting, Insight
-->
{% else %}
else
{% endif %}
{% endfor %}
With the above, it just prints out the {{ topics }}, even though Insight isn't in the all_tags array.
Note: Tagging Jinja2 as the syntax is similar

Answer 1

A combination of the filter reject and the built in test in could help you achieve this.
Sadly, it seems the reject filter does not accept negating a test, still, you can reject all the elements of topics that are not in all_tags then reject the said elements from the topics list.
So that ends with:
{{ topics | reject('in', topics | reject('in', all_tags) | list) | list }}
Switch yields:
[
"Data",
"Accounting"
]