How to map scalar twig filter to array

Question

I have a simple array of floats. And I need to show it as comma separated string.

{{ arr|join(', ') }}

is bad solution because of excessive insignificant accuracy.

{% for val in arr %}
    {{val|number_format(2)}},
{% endfor %}

is bad because of extra comma at the end.

I would like to do something like this:

{{ arr|map(number_format(3))|join(', ') }}

but I have not found filter map or similar filter it Twig. Аnd I don't know how to implement such filter.

Emlen

You can add existing functions to twig – Velarde

Answer 1

Quick Answer (TL;DR)

• This question relates to higher-order functions
  • Map is a higher-order function
  • (see eg) https://en.wikipedia.org/wiki/Map_(higher-order_function)
  • (see eg) https://en.wikipedia.org/wiki/Higher-order_function

Detailed Answer

Context

• Twig 2.x (latest version as of Wed 2017-02-08)

Problem

• Scenario: DeveloperGarricSugas wishes to apply higher-order function(s) to a Twig variable
  • Higher order functions allow any of various transformations on any Twig variable
• Twig support for higher-order functions is limited
• Nevertheless, there exist addon libraries for this
  • (see eg) https://github.com/dpolac/twig-lambda
• Custom filters or functions can also be used to simulate this

Example

• DeveloperGarricSugas starts with a sequentially-indexed array
• transform from BEFORE into AFTER (uppercase first letter)

{%- set mylist = ['alpha','bravo','charlie','delta','echo']  -%}

BEFORE: 
['alpha','bravo','charlie','delta','echo']

AFTER: 
['Alpha','Bravo','Charlie','Delta','Echo']

Solution

{%- set mylist = mylist|map(=> _|capitalize)  -%}    

Pitfalls

• Twig higher-order functions limited support comes from addon-libraries
• The above solution does not work with native Twig

See also

• https://twigfiddle.com/rsl89m
• https://github.com/dpolac/twig-lambda

Solidago

Please correct syntax: mylist|map(=> _|capitalize) – Emlen

It looks as though there is now a version of map, with slightly different syntax, in Twig core. symfony.com/blog/twig-adds-filter-map-and-reduce-features – Tahoe

Answer 2

Why not use the loop variable?

{% for val in arr %}
    {{val|number_format(2)}}
    {% if not loop.last %}, {% endif %}
{% endfor %}

Bacchus

OK, this is the solution for my example. But this is not a solution for the subject topic. You prefer to write a new analogue of an existing filter join... But can't we use the standard join filter for this? – Emlen

You can write a new filter to use array_map under the hood, but join has no such functionality. – Bacchus

Answer 3

Quick Answer (TL;DR)

• alternate approach is to use Twig loops (workaround)

Workaround

{%- set aaold = [1.234,234.56,11.222,22.333]  -%}
{%- set aanew = []  -%}
{% for item in aaold -%}
  {{ aanew|merge(item|number_format(3)) }}
{% endfor %}
{{ aanew | join(', ') }}

Pitfalls

• requires use of array|merge
  • alternative to array|merge ... loop.first or loop.last as specified here
• requires addition of loop control structure that means extra code bloat

Solidago