keys
The keys
filter returns the keys of a sequence or a mapping. It is useful
when you want to iterate over the keys of a sequence or a mapping:
1 2 3 4 5 6 7 8 9
{% for key in [1, 2, 3, 4]|keys %}
{{ key }}
{% endfor %}
{# outputs: 1 2 3 4 #}
{% for key in {a: 'a_value', b: 'b_value'}|keys %}
{{ key }}
{% endfor %}
{# outputs: a b #}
Note
Internally, Twig uses the PHP array_keys function.