how to get the last 3 elements with specific name value with JMESPATH and javascript?

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I have the below json data array:

[{"name":"Button1","date":"1596959802144"},{"name":"Button2","date":"1596959804238"},{"name":"Button3","date":"1596959809334"},{"name":"Button1","date":"1597000878135"},{"name":"Button2","date":"1597000896335"},{"name":"Button3","date":"1597000901536"},{"name":"Button2","date":"1597000904437"},{"name":"Button3","date":"1597000909535"},{"name":"Button1","date":"1597000912250"},{"name":"Button2","date":"1597000939937"},{"name":"Button3","date":"1597000957940"},{"name":"Button2","date":"1597000964640"},{"name":"Button1","date":"1597001005141"},{"name":"Button2","date":"1597001010240"},{"name":"Button3","date":"1597001014845"},{"name":"Button2","date":"1597001021644"},{"name":"Button1","date":"1597001025738"},{"name":"Button2","date":"1597001049030"},{"name":"Button3","date":"1597001054139"},{"name":"Button1","date":"1597001057741"},{"name":"Button2","date":"1597001060340"},{"name":"Button3","date":"1597001062445"},{"name":"Button1","date":"1597002599045"},{"name":"Button1","date":"1597002604128"},{"name":"Button1","date":"1597002609546"},{"name":"Button1","date":"1597002613435"},{"name":"Button1","date":"1597002681736"},{"name":"Button1","date":"1597002690843"},{"name":"Button1","date":"1597002694136"},{"name":"Button1","date":"1597002696349"},{"name":"Button1","date":"1597002699243"}]

and I would like to use JMESPath javascript library to get only the last 3 entries per each distinct name value. For example:

[{"name":"Button3","date":"1597001014845"},{"name":"Button2","date":"1597001021644"},{"name":"Button2","date":"1597001049030"},{"name":"Button3","date":"1597001054139"},{"name":"Button2","date":"1597001060340"},{"name":"Button3","date":"1597001062445"},{"name":"Button1","date":"1597002694136"},{"name":"Button1","date":"1597002696349"},{"name":"Button1","date":"1597002699243"}]

So the last 3 occurrences fro each name = Button*

checking on stackOverflow and I saw that with JQ is possible to do using this function: map_values(delpaths(keys_unsorted[:-2] | map([.])))

Get last N elements for each item of a JSON object

Is there any way to do? or using other javascript module?

jmespath json javascript
1 Answers

If you don't care about the order in your resulting array, here would be a pure JavaScript way to do this:

const getLastNForEveryName = (arr, n) => {
  const lastNOfEach = arr.reduce((acc, curr) => {
    if(acc[curr.name] == null) { // If the key doesnt exist yet, create it with the current item in the array
      acc[curr.name] = [curr]; 
    } else {
      if(acc[curr.name].length >= n) // If the array is as big as the desired size alread, remove the first added one
        acc[curr.name].shift();

      acc[curr.name].push(curr); // push the current item in the array
    }
    return acc;
  }, {})
  
  return Object.values(lastNOfEach).flatMap(l => l); // Just get the values of the object and flatMap it, so that we dont have arrays of arrays
}



// Testing
const values = [{"name":"Button1","date":"1596959802144"},{"name":"Button2","date":"1596959804238"},{"name":"Button3","date":"1596959809334"},{"name":"Button1","date":"1597000878135"},{"name":"Button2","date":"1597000896335"},{"name":"Button3","date":"1597000901536"},{"name":"Button2","date":"1597000904437"},{"name":"Button3","date":"1597000909535"},{"name":"Button1","date":"1597000912250"},{"name":"Button2","date":"1597000939937"},{"name":"Button3","date":"1597000957940"},{"name":"Button2","date":"1597000964640"},{"name":"Button1","date":"1597001005141"},{"name":"Button2","date":"1597001010240"},{"name":"Button3","date":"1597001014845"},{"name":"Button2","date":"1597001021644"},{"name":"Button1","date":"1597001025738"},{"name":"Button2","date":"1597001049030"},{"name":"Button3","date":"1597001054139"},{"name":"Button1","date":"1597001057741"},{"name":"Button2","date":"1597001060340"},{"name":"Button3","date":"1597001062445"},{"name":"Button1","date":"1597002599045"},{"name":"Button1","date":"1597002604128"},{"name":"Button1","date":"1597002609546"},{"name":"Button1","date":"1597002613435"},{"name":"Button1","date":"1597002681736"},{"name":"Button1","date":"1597002690843"},{"name":"Button1","date":"1597002694136"},{"name":"Button1","date":"1597002696349"},{"name":"Button1","date":"1597002699243"}];

console.log(getLastNForEveryName(values, 3));

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