Spartacus38 - 1 year ago 105

Ruby Question

I have a hash, that I select all the data for a dashboard to display performance, since displaying the latest value isn't always helpful, I'm trying to select the last 4 values from a hash.

I have attempted the

`thing.last(4)`

Code is below, essentially trying to display the last 4 from

`top_points`

Note: Ruby 1.9

`metric.sort.each do |key, value|`

top_point = { x: Time.parse(key).to_time.to_i, y: value['top_10'] }

top_points << top_point

average_point = { x: Time.parse(key).to_time.to_i, y: value['average'] }

average_points << average_point

end

Answer Source

in order to get the last four elements of your hash, you should first `map`

it as an array, get the indexes desired and then transform again the array into an hash.

For example:

```
2.2.1 :001 > hash = {a: 1, b: 2, c: 3, d: 4, e: 5}
=> {:a=>1, :b=>2, :c=>3, :d=>4, :e=>5}
2.2.1 :002 > hash.map{|h| h}[-4..-1].to_h
=> {:b=>2, :c=>3, :d=>4, :e=>5}
```

In your specific case, the code might look like this:

```
metric.sort.map{|h| h}[-4..-1].to_h.each do |key, value|
top_point = { x: Time.parse(key).to_time.to_i, y: value['top_10'] }
top_points << top_point
average_point = { x: Time.parse(key).to_time.to_i, y: value['average'] }
average_points << average_point
end
```

Another way to write it could be:

```
last_four_metrics = metric.sort.map{|h| h}[-4..-1].to_h
top_points = last_four_metrics.map{|k, v| { x: Time.parse(k).to_time.to_i, y: v['top_10'] }}
average_points = last_four_metrics.map{|k, v| { x: Time.parse(k).to_time.to_i, y: v['average'] }}
```

Update: compatibility with Ruby 1.9

```
last_four_metrics = Hash[ metric.sort.map{|h| h}[-4..-1] ]
top_points = last_four_metrics.map{|k, v| { x: Time.parse(k).to_time.to_i, y: v['top_10'] }}
average_points = last_four_metrics.map{|k, v| { x: Time.parse(k).to_time.to_i, y: v['average'] }}
```