Twig Adds Filter, Map and Reduce Features

Filter, map and reduce

Contributed by
Fabien Potencier
in #2996.

The "filter, map and reduce" pattern is getting more and more popular in other programming languages and paradigms (e.g. functional programming) to transform collections and sequences of elements. You can now use them in Twig thanks to the new filter, map and reduce filters in combination with the new arrow function.

The filter filter removes from a sequence all the elements that don't match the given expression. For example, to ignore products without enough stock:

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{% for product in related_products|filter(product => product.stock > 10) %}
    {# ... #}
{% endfor %}

The arrow function receives the value of the sequence or mapping as its argument. The name of this argument can be freely chosen and it doesn't have to be the same as the variable used to iterate the collection:

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{% for product in related_products|filter(p => p.id not in user.recentPurchases) %}
    {# ... #}
{% endfor %}

If you also need the key of the sequence element, define two arguments for the arrow function (and wrap them in parenthesis):

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{% set components = all_components|filter(
    (v, k) => v.published is true and not (k starts with 'Deprecated')
) %}

Thanks to the new filter option, the if condition is no longer needed for the for loops, so we've deprecated it in favor of always using filter:

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-{% for product in related_products if product.stock > 10 %}
+{% for product in related_products|filter(p => p.stock > 10) %}
    {# ... #}
{% endfor %}

If you prefer to keep using the for ... if pattern, include the if in the for loop:

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{% for product in related_products %}
    {% if product.stock > 10 %}
        {# ... #}
    {% endif %}
{% endfor %}

The map filter applies an arrow function to the elements of a sequence or a mapping (it's similar to PHP's array_map()):

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{% set people = [
    {first: "Alice", last: "Dupond"},
    {first: "Bob", last: "Smith"},
] %}

{{ people|map(p => p.first ~ ' ' ~ p.last)|join(', ') }}
{# outputs Alice Dupond, Bob Smith #}

The reduce filter iteratively reduces a sequence or a mapping to a single value using an arrow function. Because of this behavior, the arrow function always receives two arguments: the current value and the result of reducing the previous elements (usually called "carry"):

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{% set num_products = cart.rows|reduce((previousTotal, row) => previousTotal + row.totalUnits) %}
{{ num_products }} products in total.

In addition to filter, map and reduce, recent Twig versions have added other useful filters and tags.

The "column" filter

Contributed by
Pablo Schläpfer
in #2992.

This new column filter returns the values from a single column in the given array (internally it uses the PHP array_column() function):

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Your oldest friend is {{ max(user.friends|column('age')) }} years old.

The "apply" tag

Contributed by
Fabien Potencier
in #2977.

The filter tag has been deprecated (to not confuse it with the new filter filter explained above) and it has been replaced by the new apply tag which works exactly the same as the previous tag:

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-{% filter upper %}
+{% apply upper %}
    This text becomes uppercase.
{% endapply %}

Allowed using Traversable objects

Contributed by
Ondřej Exner
in #3016.

Another important change related to filters and tags is that you can now use objects that implement the Traversable PHP interface everywhere you can use iterators or arrays: the with tag, the with argument of the include and embed tags, the filter filter, etc.