mirror of
https://github.com/jbranchaud/til
synced 2026-01-03 15:18:01 +00:00
30 lines
849 B
Markdown
30 lines
849 B
Markdown
# Map With Index Over An Array
|
|
|
|
The [`#map`](https://devdocs.io/ruby~2.5/enumerable#method-i-map) method on its
|
|
own allows you to interact with each item of an array, producing a new array.
|
|
|
|
```ruby
|
|
[1,2,3].map { |item| item * item }
|
|
#=> [1,4,9]
|
|
```
|
|
|
|
If you also want access to the index of the item, you'll need some help from
|
|
other enumerable methods. As of Ruby 1.9.3, you can chain on
|
|
[`#with_index`](https://devdocs.io/ruby~2.5/enumerator#method-i-with_index):
|
|
|
|
```ruby
|
|
[1,2,3].map.with_index { |item, index| item * index }
|
|
#=> [0,2,6]
|
|
```
|
|
|
|
This method has the added benefit of allowing you to specify the starting value
|
|
of the index. It normally starts with `0`, but you could just as easily start
|
|
at `1`:
|
|
|
|
```ruby
|
|
[1,2,3].map.with_index(1) { |item, index| item * index }
|
|
#=> [1,4,9]
|
|
```
|
|
|
|
[source](https://stackoverflow.com/a/11280903/535590)
|