There is an array of JavaScript:
let arr=[
[220,A,12],
[560,B,5],
[300,A,0],
[300,H,3],
[300,K,T],
[450,P,9],
[500,E,6],
[500,M,8]
];
The first element of sub-arrays have some repeated values,
I want to find them and modify the repeated values, as follow:
[300,A,0], ===> remain unchanged
[300,H,3], ===> [320,H,3], //First element add 20
[300,K,T], ===> [340,K,T], //First element add 20 again
[500,E,6], ===> remain unchanged
[500,M,8] ===> [520,M,8] //First element add 20
That is, the first element adds 20 in proper order if repeated.
Other elements don't need to be considered.
How to do it in javaScript?
One option is to use reduce. I pass an object as the initial value to reduce:
{
last: null, // The previous number encountered
offset: 20, // The amount to add on repeat
data: [] // The new array
}
Then, use this to build the new array:
let arr=[
[220,'A',12],
[560,'B',5],
[300,'A',0],
[300,'H',3],
[300,'K','T'],
[450,'P',9],
[500,'E',6],
[500,'M',8]
];
arr = arr.reduce((prev, cur) => {
// Is this a repeat?
if (prev.last == cur[0]) {
cur[0] += prev.offset;
prev.offset += 20;
}
// Not a repeat. Reset.
else {
prev.last = cur[0];
prev.offset = 20;
}
prev.data.push(cur);
return prev;
}, {last: null, offset: 20, data: []}).data;
console.log(arr);using map key:value, where key is number and value is its occurrence so far
let arr = [
[220, 12],
[560, 5],
[300, 0],
[300, 3],
[300, 0],
[450, 9],
[500, 6],
[500, 8]
];
m = {}
for (let i = 0; i < arr.length; ++i) {
const x = arr[i][0]
if (m[x] > 0){
arr[i][0] += (m[x]) *20
m[x]++
} else m[x] = 1
}
console.log(arr)