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.

Answer 1

Why not use the loop variable?

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

Answer 2

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

Example01

• 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