Reduce Filter and Arrow Functions in Twig

Using the same data that is includ­ed in the pre­vi­ous video, Andrew shows how to use the reduce fil­ter in Twig. 

To demon­strate how to use the reduce fil­ter, Andrew seeks to find the total val­ue of all of the items in the data set.

Find Total Val­ue Using a Loop

We’ll start by imple­ment­ing it with a loop:

    {% set totalValue = 0 %}
    {% for item in ryansGoBag %}
        {% set totalValue = totalValue + item.value * (conversionRates[item.name] ?? 1.0) %}
    {% endfor %}
    {% set totalValue = totalValue | currency('USD') %}

    {% dd totalValue %}

Find Total Val­ue Using reduce

We know that reduce is a bet­ter way to tal­ly up the val­ues of the items in the data set. We drop the loop and imple­ment the reduce filter. 

    {% set totalValue = ryansGoBag | reduce(
        (carry, item) => carry + item.value * (conversionRates[item.name] ?? 1.0),
        0
        )
        | currency('USD') %}

    {% dd totalValue %}

Find Total Val­ue Using reduce and Craft Closure

We keep the reduce fil­ter but add an arrow vari­able using Craft Clo­sure. Pret­ty sweet!

    {% set totalAmountArrow = (carry, item) => carry + item.value * (conversionRates[item.name] ?? 1.0) %}
    {% set totalValue = ryansGoBag | reduce(totalAmountArrow, 0) | currency('USD') %}

    {% dd totalValue %}

Anoth­er use of the reduce fil­ter is to get a list of the types of items in the data set. How­ev­er, we only want a type list­ed once, not mul­ti­ple times.

Get Types of Items Using Loop

    {% set types = [] %}
    {% for item in ryansGoBag %}
        {% if item.type not in types %}
            {% set types = types | merge([item.type]) %}
        {% endif %}
    {% endfor %}

    {% dd types %}

Get Types of Items Using reduce

In this exam­ple, we drop the for-loop and replace it with a reduce fil­ter using an arrow function.

    {% set types = ryansGoBag | reduce(
        (carry, item) => item.type in carry ? carry : carry | merge([item.type]),
        []
        ) %}

    {% dd types %}

Get Types of Items Using reduce and Craft Closure

Final­ly, we use reduce, an arrow func­tion with an arrow vari­able avail­able to us via Craft Closure:

    {% set typesArrow = (carry, item) => item.type in carry ? carry : carry | merge([item.type]) %}
    {% set types = ryansGoBag | reduce(typesArrow, []) %}

    {% dd types %}