Array Reduce examples and use cases

reduce.js

// Flatten array
var flattened = [[0, 1], [2, 3], [4, 5]].reduce(
  ( accumulator, currentValue ) => accumulator.concat(currentValue),
  []
);
// flattened is [0, 1, 2, 3, 4, 5]


// Remove duplicate items in an array
let arr = [1, 2, 1, 2, 3, 5, 4, 5, 3, 4, 4, 4, 4];
let result = arr.sort().reduce((accumulator, current) => {
    const length = accumulator.length
    if (length === 0 || accumulator[length - 1] !== current) {
        accumulator.push(current);
    }
    return accumulator;
}, []);
console.log(result); //[1,2,3,4,5]