Twig Adds Filter, Map and Reduce Features
June 20, 2019 • Published by Javier Eguiluz
Twig is the template language used in Symfony and thousands of other projects. In the last six months alone, Twig has released 30 versions for its 1.x and 2.x branches, adding lots of interesting new features. This article focuses on some of the new filters and tags added recently.
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):
1
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.
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Comments are closed.
To ensure that comments stay relevant, they are closed for old posts.
I like the changes, but did you test them on frontend coders? For example, I've managed to explain this one to ours:
because it's like English. He can read and write it.
The replacement is going to take a bit more education, because now I have to explain what a filter is and the new syntax. He's not a JavaScript programmer, he's a HTML and CSS coder.
If Twig's audience is wider than programmers, please keep the old syntax alongside the new filter.
This is certainly nice, but I can't help but feel that filter/map/reduce are something you probably should avoid in a template. They can be abused quickly and risk letting inexperienced developers add business logic in a template.
These features are useful and I missed them here and there. However, there is an important question to answer: How much damage can average coder do with them?
There should be a big fat warning that you should not do this in template and a proper example how it should be done right.
This is a nice addition that removes the need to use a bundle (https://github.com/dpolac/twig-lambda). However, I tried using it recently and found something that looks like a bug. I have detailed the issue at https://stackoverflow.com/questions/56448878/cant-iterate-the-filter-filter-multiple-times but unfortunately got no reply.
@Peter You are not forced to use the next syntax. Using an "if" tag in a "for" loop is still possible and probably clearer for many. We have removed the "if" support on the "for" tag as it was confusing for people as there are some edge cases that made it quite annoying to use/explain/debug.
@Davide They are available for display and not for implementing some business logic. But that's true with almost all other features (even a "for" loop is sometimes not something you should use in a template).
@Josef You cannot cause any damage using those new filters. As for examples, there are plenty in the docs. So, not sure what we can change here. Any ideas?
@Jean-Guilhem This was a bug that has been fixed now.
@Peter, I've updated the blog post to show the alternative "for ... if" pattern mentioned by Fabien that doesn't use the filter and arrow function.
@Fabien, nice, thanks!
Great addition - I can already see how this can save us from having to 1) spit out our twig variables into js in order to map/reduce/etc 2) perform various tasks in php and have multiple variations as twig variables.
Awesome!
So glad you removed the for if weird yoda style already love the filter and map function :-)
👍