slice

The slice filter extracts a slice of a sequence, a mapping, or a string:

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{% for i in [1, 2, 3, 4, 5]|slice(1, 2) %}
    {# will iterate over 2 and 3 #}
{% endfor %}

{{ '12345'|slice(1, 2) }}

{# outputs 23 #}

You can use any valid expression for both the start and the length:

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{% for i in [1, 2, 3, 4, 5]|slice(start, length) %}
    {# ... #}
{% endfor %}

As syntactic sugar, you can also use the [] operator:

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{% for i in [1, 2, 3, 4, 5][start:length] %}
    {# ... #}
{% endfor %}

{{ '12345'[1:2] }} {# will display "23" #}

{# you can omit the first argument -- which is the same as 0 #}
{{ '12345'[:2] }} {# will display "12" #}

{# you can omit the last argument -- which will select everything till the end #}
{{ '12345'[2:] }} {# will display "345" #}

{# you can use a negative value -- for example to remove characters at the end #}
{{ '12345'[:-2] }} {# will display "123" #}

The slice filter works as the array_slice PHP function for arrays and mb_substr for strings with a fallback to substr.

If the start is non-negative, the sequence will start at that start in the variable. If start is negative, the sequence will start that far from the end of the variable.

If length is given and is positive, then the sequence will have up to that many elements in it. If the variable is shorter than the length, then only the available variable elements will be present. If length is given and is negative then the sequence will stop that many elements from the end of the variable. If it is omitted, then the sequence will have everything from offset up until the end of the variable.

The argument preserve_keys is used to reset the index during the loop.

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{% for key, value in [1, 2, 3, 4, 5]|slice(1, 2, true) %}
    {{ key }} - {{ value }}
{% endfor %}

{# output
    1 - 2
    2 - 3
#}

{% for key, value in [1, 2, 3, 4, 5]|slice(1, 2) %}
    {{ key }} - {{ value }}
{% endfor %}

{# output
    0 - 2
    1 - 3
#}