Get last occurrence of item in array of arrays (Javascript)

Question

I have the following array:

[[ "7", "4" ], [ "7", "43" ], [ "7", "4" ], [ "7", "" ], [ "6", "2" ], [ "7", "8" ] ]

How can I get the last occurrence of each distinct first element.

I would need the above array to be converted into:

[ [ "6", "2" ], [ "7", "8" ] ]

Answer 1

Use Map and use the first element as a key:

 const data = [[ "7", "4" ], [ "7", "43" ], [ "7", "4" ], [ "7", "" ], [ "6", "2" ], [ "7", "8" ] ]; const result = Array.from(data.reduce((acc, item) => { acc.set(item[0], item) return acc; }, new Map()).values()); console.log(result);