join

The join filter returns a string which is the concatenation of the items of a sequence:

1
2

{{ [1, 2, 3]|join }}
{# returns 123 #}

The separator between elements is an empty string per default, but you can define it with the optional first parameter:

1
2

{{ [1, 2, 3]|join('|') }}
{# outputs 1|2|3 #}

A second parameter can also be provided that will be the separator used between the last two items of the sequence:

1
2

{{ [1, 2, 3]|join(', ', ' and ') }}
{# outputs 1, 2 and 3 #}