I'd like to combine identical elements in an array, into a single term with how many times the value appears
function combineArrayElements(arr) {
return arr.map((e, i, ar) => {
if (e === ar[i + 1] || (e[0] && e[0] === ar[i + 1])) {
return [e, e[1] + 1]
}
return e;
})
}
Some example input and output:
// input [3, 2, 2, 5, 1, 1, 7, 1]
// output [3,[2,2],5,[1,2],7,1]
// input [1, 1, 1, 2, 1]
// output [[1,3], 2, 1]
You could reduce the array and if the value is equal the last value, take an array and increment the counter.
const
getGrouped = array => array.reduce((r, v, i, { [i - 1]: last }) => {
if (v === last) {
if (!Array.isArray(r[r.length - 1])) r[r.length - 1] = [r[r.length - 1], 1];
r[r.length - 1][1]++;
} else {
r.push(v);
}
return r;
}, []);
console.log(getGrouped([3, 2, 2, 5, 1, 1, 1, 7, 1]));
console.log(getGrouped([2, 2, 2, 3]));Thank, Joseph Cho - answer is:
function splitCounts(arr) {
let res = [];
let count = 1;
for (let i=0; i<arr.length; i++) {
if (arr[i] === arr[i+1]) {
count++;
} else {
res.push([arr[i], count]);
count = 1;
}
}
return res;
}
// [[3,1],[2,2],[5,1],[1,2],[7,1],[1,1]]
console.log(splitCounts([3,2,2,5,1,1,7,1]));
Refactored Nina Scholz's answer with longer variable names, comments, and slightly different control of flow:
const combineAdjacentElements = array => array.reduce((acc, val, i) => {
// if cur is different from prev value, add raw number
if (val !== array[i - 1]) {
acc.push(val)
return acc
}
// if first repetition, replace val with grouped array
if (typeof acc.at(-1) === 'number') {
acc[acc.length - 1] = [val, 2];
return acc
}
// if multiple repetition, increment counter in grouped array
acc.at(-1)[1]++;
return acc;
}, []);
const output = combineAdjacentElements([3, 2, 2, 2, 5, 1, 1, 7, 1])
console.log(JSON.stringify(output, null, 0))
// [3,[2,3],5,[1,2],7,1]