Creating dynamic array and set keys
You can do this using the twig attribute function:

{% set data = [
    {'column':'1','title':'Quick Facts'}, 
    {'column':'2','title':'Inspiration'}, 
    {'column':'1','title':'Agencies'}, 
    {'column':'2','title':'Industry Experience'}
] %}

{% set cols = {} %}
{% for item in data %}

    {# create a dynamic property if one doesn't exist #}
    {% if not attribute(cols, 'col' ~ item.column) is defined %}
        {% set cols = cols|merge({ ('col' ~ item.column) : [item.title] }) %}

    {# else update the dynamic property with the new title #}
    {% else %}
        {% set titles = attribute(cols, 'col' ~ item.column) %}
        {% set titles = titles|merge([item.title]) %}
        {% set cols = cols|merge({ ('col' ~ item.column) : titles }) %}

    {% endif %}
{% endfor %}

{{ dump(cols) }}

{#
array(2) { 
    ["col1"]=&gt; array(2) {
         [0]=&gt; string(11) "Quick Facts" 
         [1]=&gt; string(8) "Agencies" 
    } 
    ["col2"]=&gt; array(2) { 
        [0]=&gt; string(11) "Inspiration" 
        [1]=&gt; string(19) "Industry Experience" 
    } 
} 
#}