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.

Accepted Answer

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