# How to functionally increase number in array if previous one is lower

I have array of numbers that decreases, but I want it never to decrease:

`const numbers =[0,1,2,3,4,5,1, 2];`

Desired result is:

`[0, 1, 2, 3, 4, 5, 5, 5]`

I know how to achieve it with for loop:

``````for (let index = 0; index < numbers.length; index++) {
const element = numbers[index];
if (index > 0) {
const prevEl = numbers[index - 1];
if (element < prevEl) {
numbers[index] = prevEl;
}
}
}

``````

But when using map

``````numbers.map((item, index) => {
const prevEl = numbers[index - 1];
if (item < prevEl) {
return prevEl;
}
return item;
})
``````
``````const numbers = [0,1,2,3,4,5,1, 2];

const result = numbers.map((item, index) => {
const prevEl = numbers[index - 1];
if (item < prevEl) {
return prevEl;
}
return item;
});

console.log(result); // [0, 1, 2, 3, 4, 5, 5, 2]``````

I get this instead: `[0, 1, 2, 3, 4, 5, 5, 2]`

What would be the functional way to achieve this?

### >Solution :

You could use `Math.max` between the current and the preceding entries in the list:

``````const numbers = [0,1,2,3,4,5,1, 2];

result = numbers.map((v, i, a) => Math.max(v, ...a.slice(0, i)))
console.log(result)``````