collections.Index

collections.Index COLLECTION INDEXES

collections.Index COLLECTION KEYS

any

index

The index functions returns the result of indexing its first argument by the following arguments. Each indexed item must be a map or a slice, e.g.:

{{ $slice := slice "a" "b" "c" }}
{{ index $slice 0 }} → a
{{ index $slice 1 }} → b

{{ $map := dict "a" 100 "b" 200 }}
{{ index $map "b" }} → 200

The function takes multiple indices as arguments, and this can be used to get nested values, e.g.:

{{ $map := dict "a" 100 "b" 200 "c" (slice 10 20 30) }}
{{ index $map "c" 1 }} → 20
{{ $map := dict "a" 100 "b" 200 "c" (dict "d" 10 "e" 20) }}
{{ index $map "c" "e" }} → 20

You may write multiple indices as a slice:

{{ $map := dict "a" 100 "b" 200 "c" (dict "d" 10 "e" 20) }}
{{ $slice := slice "c" "e" }}
{{ index $map $slice }} → 20

Example: load data from a path based on front matter parameters

Assume you want to add a location = "" field to your front matter for every article written in content/vacations/. You want to use this field to populate information about the location at the bottom of the article in your single.html template. You also have a directory in data/locations/ that looks like the following:

data/
  └── locations/
      ├── abilene.toml
      ├── chicago.toml
      ├── oslo.toml
      └── provo.toml

Here is an example:

pop_city: 658390
pop_metro: 1717900
website: https://www.oslo.kommune.no

pop_city = 658390
pop_metro = 1717900
website = 'https://www.oslo.kommune.no'

{
   "pop_city": 658390,
   "pop_metro": 1717900,
   "website": "https://www.oslo.kommune.no"
}

The example we will use will be an article on Oslo, whose front matter should be set to exactly the same name as the corresponding file name in data/locations/:

---
location: oslo
title: My Norwegian Vacation
---

+++
location = 'oslo'
title = 'My Norwegian Vacation'
+++

{
   "location": "oslo",
   "title": "My Norwegian Vacation"
}

The content of oslo.toml can be accessed from your template using the following node path: .Site.Data.locations.oslo. However, the specific file you need is going to change according to the front matter.

This is where the index function is needed. index takes 2 arguments in this use case:

1. The node path
2. A string corresponding to the desired data; e.g.—

{{ index .Site.Data.locations "oslo" }}

The variable for .Params.location is a string and can therefore replace oslo in the example above:

{{ index .Site.Data.locations .Params.location }}
=> map[website:https://www.oslo.kommune.no pop_city:658390 pop_metro:1717900]

Now the call will return the specific file according to the location specified in the content’s front matter, but you will likely want to write specific properties to the template. You can do this by continuing down the node path via dot notation (.):

{{ (index .Site.Data.locations .Params.location).pop_city }}
=> 658390