Check consecutive numbers in array javascript

Question

There is a array like this on my hand;

var array = [{value:"0"},{value:"1"},{value:"2"},{value:"3"},{value:"4"}];

I need check, this numbers is going consecutive?

[{value:"0"},{value:"1"},{value:"2"},{value:"3"},{value:"4"}];
TRUE (0,1,2,3,4)

[{value:"0"},{value:"1"},{value:"2"},{value:"3"},{value:"5"}];
FALSE (0,1,2,3,5)

Your object inside array is not valid for your task and look like [{ value: "4" }] — Nikita Madeev
– Nikita Madeev, Commented Jul 21, 2020 at 7:15
The array you posted contains only one item: an invalid object. An object cannot have multiple keys having the same name. — axiac
– axiac, Commented Jul 21, 2020 at 7:17

adiga · Accepted Answer · 2020-07-21 07:37:45Z

3

You could check if every item is one more than the previous item. This will stop looping once a non-consecutive values is found

array.every(({ value }, i) => i === 0 || +value === +array[i-1].value + 1)

Here's a snippet:

function isConsecutive(array) {
  return array.every(({ value }, i) => i === 0 || +value === +array[i-1].value + 1)
}

console.log(
  isConsecutive([{value:"0"},{value:"1"},{value:"2"},{value:"3"},{value:"4"}]),
  isConsecutive([{value:"0"},{value:"1"},{value:"3"}])
)

answered Jul 21, 2020 at 7:37

adiga

35.4k9 gold badges65 silver badges88 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Yevhen Horbunkov Over a year ago

This won't work for empty array or single array item, as well as descending order (OP didn't state whether this is the case, though).

Fernando Flores Jan 13 at 21:27

@YevhenHorbunkov "every" returns true for an empty array

Yevhen Horbunkov Jan 14 at 17:13

@FernandoFlores: the point being made was that the empty array unlikely qualifies as an array of consecutive numbers.

Fernando Flores Jan 14 at 23:44

@YevhenHorbunkov I don't think so... Do you know about the vacuous truth?

adiga Jan 15 at 10:50

@YevhenHorbunkov This was not the input provided in the question and can easily be fixed by adding a length check. The goal of these answers is to guide the OP in the right direction. There could be many edge cases where the source is empty, or null, or undefined, or the nested object doesn't have value property etc

Nikita Madeev · Accepted Answer · 2020-07-21 07:24:24Z

2

You can use reduce with the initial value as the first element of the array

const checkIsConsecutive = (array) =>
    Boolean(array.reduce((res, cur) => (res ? (Number(res.value) + 1 === Number(cur.value) ? cur : false) : false)));

console.log(checkIsConsecutive([{ value: '0' }, { value: '1' }, { value: '2' }, { value: '3' }, { value: '4' }]));
console.log(checkIsConsecutive([{ value: '0' }, { value: '1' }, { value: '2' }, { value: '3' }, { value: '5' }]));

answered Jul 21, 2020 at 7:24

Nikita Madeev

4,49012 silver badges23 bronze badges

2 Comments

Yevhen Horbunkov Over a year ago

This will fail for a single item in array or empty array and won't work for descending order (OP didn't state whether this is the case, though).

Yevhen Horbunkov Over a year ago

@YavuzSelimÖzmen : while above solution fails for the whole bunch of edge cases just like .every()-based method, the former works much slower as it will loop throughout the entire array, whereas .every() exits upon first non-consecutive value

Tom · Accepted Answer · 2020-07-21 10:45:13Z

The other answer are really well made, and look very pleasing. However as @Yevgen Gorbunkov mentioned, they do not take empty arrays, single item arrays, as well as desc order.

I am quite new to JS so the answer is not optimal and can most likely be improved. But I figured giving it a shot wouldn't hurt.

Attempt 1: jsfiddle

//var arrr = [{value:"0"}];
var arrr = [{value:"8"},{value:"7"},{value:"6"},{value:"5"},{value:"4"},{value:"3"},{value:"2"},{value:"1"},{value:"0"}];
//var arrr = [{value:"8"},{value:"3"},{value:"6"},{value:"5"},{value:"4"},{value:"3"},{value:"2"},{value:"1"},{value:"0"}];
//var arrr = [];
//var arrr = [{value:"0"},{value:"1"},{value:"2"},{value:"3"},{value:"4"},{value:"5"},{value:"6"},{value:"7"},{value:"8"}];

var arr = arrr.map(function (obj) {
  return Number(obj.value);
});

isConsecutive(arr);
 
 function isConsecutive(arr) {
 
  var consecutive;
  let previousAsc = arr[0];
  let previousDesc = arr[0];
  let firstAsc;
  let firstDesc;
  
  for (let i = 1; i < arr.length; i++) {
    if ((previousDesc - 1) !== arr[i]) {
      if ((previousAsc + 1) !== arr[i]) {
        firstAsc = arr[i];
        consecutive = false;
        break;
      } else {
        consecutive = true;
            previousDesc --;
            previousAsc ++;
      }
    
    } else {
            consecutive = true;
            previousDesc --;
            previousAsc ++;
    }
  }
  console.log(consecutive)
}

Attempt 2: jsfiddle

//var arrr = [{value:"0"}];
var arrr = [{value:"8"},{value:"7"},{value:"6"},{value:"5"},{value:"4"},{value:"3"},{value:"2"},{value:"1"},{value:"0"}];
//var arrr = [{value:"8"},{value:"3"},{value:"6"},{value:"5"},{value:"4"},{value:"3"},{value:"2"},{value:"1"},{value:"0"}];
//var arrr = [];
//var arrr = [{value:"0"},{value:"1"},{value:"2"},{value:"3"},{value:"4"},{value:"5"},{value:"6"},{value:"7"},{value:"8"}];

var arr = arrr.map(function (obj) {
  return Number(obj.value);
});
var arrSort = arrr.map(function (obj) {
  return Number(obj.value);
});

if(arr && arr.length >= 2){

  if(JSON.stringify(arrSort.sort()) === JSON.stringify(arr) || JSON.stringify(arrSort.sort().reverse()) === JSON.stringify(arr)){
    /* console.log(arrSort.sort().reverse());
        console.log(arr); */
    console.log("Array is consecutive")
  } else {
    /* console.log(arrSort.sort());
        console.log(arr); */
    console.log("Array is not consecutive")
  }
} else {
    console.log("array does not exist or does not have enough values to start")
}

Firmin Martin · Accepted Answer · 2022-05-11 04:25:13Z

Here is an auxiliary function that computes the length of the most long subarray of an array.

const maxConsecutive = (arr) => {
    const result = arr.reduce((a, b) => {
        const { count, maxCount, cons } = a;
        if (cons.length === 0)
            return { count: 1, maxCount: Math.max(1, maxCount), cons: cons.concat([b]) };
        else {
            const last = cons.at(-1);
            const isCons = (b - last) === 1;
            return {
                count: isCons ? count + 1 : 0,
                maxCount: isCons ? Math.max(count + 1, maxCount) : maxCount,
                cons: isCons ? cons.concat([b]) : []
            };
        }
    }, { count: 0, maxCount: 0, cons: [] });
    return result.maxCount;
}

Sample outputs:

maxConsecutive([])
> 0
maxConsecutive([0,1,2,3,4])
> 5
maxConsecutive([0,1,2,3,5])
> 4

So now, it's pretty obvious how it can be helpful to check whether the array is consecutive or not: it suffices to maxConsecutive(arr) === arr.length.

crazy_phage · Accepted Answer · 2020-07-21 07:55:00Z

-1

Here is another way to to this.

const array = [{value:"0"},{value:"1"},{value:"2"},{value:"3"},{value:"4"}];

function isConsecutive (array) {
    const pred = array.map (i => parseInt(i.value))
    const expect = range(0, 4) // maybe use lodash.
    return pred === expect 
}

I think you do know what numbers are consecutive, so you can create a consecutive array to match your original input.

answered Jul 21, 2020 at 7:55

crazy_phage

5589 silver badges29 bronze badges

Collectives™ on Stack Overflow

Check consecutive numbers in array javascript

5 Answers 5

5 Comments

2 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

5 Comments

2 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related