Merge pull request TheAlgorithms#1039 from Shopify/where-filter-documentation

Add documentation for where filter

Author: pushrax

filters/where.md

@@ -0,0 +1,90 @@
+---
+title: where
+description: Liquid filter that selects from arrays.
+---
+
+Creates an array including only the objects with a given property value, or any [truthy]({{ "/basics/truthy-and-falsy#truthy" | prepend: site.baseurl }}) value by default.
+
+In this example, assume you have a list of products and you want to show your kitchen products separately. Using `where`, you can create an array containing only the products that have a `"type"` of `"kitchen"`.
+
+<p class="code-label">Input</p>
+{% raw %}
+```liquid
+All products:
+{% for product in products %}
+- {{ product.title }}
+{% endfor %} 
+
+{% assign kitchen_products = products | where: "type", "kitchen" %}
+
+Kitchen products:
+{% for product in kitchen_products %}
+- {{ product.title }}
+{% endfor %} 
+```
+{% endraw %}
+
+<p class="code-label">Output</p>
+```text
+All products:
+- Vacuum
+- Spatula
+- Television
+- Garlic press
+
+Kitchen products:
+- Spatula
+- Garlic press
+
+```
+
+Say instead you have a list of products and you only want to show those that are available to buy. You can `where` with a property name but no target value to include all products with a [truthy]({{ "/basics/truthy-and-falsy#truthy" | prepend: site.baseurl }}) `"available"` value.
+
+<p class="code-label">Input</p>
+{% raw %}
+```liquid
+All products:
+{% for product in products %} 
+- {{ product.title }}
+{% endfor %}
+
+{% assign available_products = products | where: "available" %}
+
+Available products:
+{% for product in available_products %} 
+- {{ product.title }}
+{% endfor %}
+
+```
+{% endraw %}
+
+<p class="code-label">Output</p>
+
+```text
+All products:
+- Coffee mug
+- Limited edition sneakers
+- Boring sneakers
+
+Available products:
+- Coffee mug
+- Boring sneakers
+
+```
+
+
+The `where` filter can also be used to find a single object in an array when combined with the `first` filter. For example, say you want to show off the shirt in your new fall collection.
+
+<p class="code-label">Input</p>
+{% raw %}
+```liquid
+{% assign new_shirt = products | where: "type", "shirt" | first %}
+
+Featured product: {{ new_shirt.title }}
+```
+{% endraw %}
+
+<p class="code-label">Output</p>
+```text
+Featured product: Hawaiian print sweater vest
+```