Print all values from array but with formatting if there are intervals

Question

I have a array of numbers. I want to print all values, but with interval if it's possible. For example:

[1,2,3,5,7,8,10]

I think you will understand what I want to get with example. For above array I want to get the following string:

"1-3, 5, 7-8, 10"

So, we have 1,2,3 in the array, then 5. The 4 is not present, so we close first interval and add to the string 1-3. Then continue, after 5 goes 7. In this case we can't create interval, therefore we just add 5. Then continue, we have 7, after 7 goes 8, after 8 goes 10, so we can create 7-8 interval only. the 10 is last so we just add it to string. In result, we have:

"1-3, 5, 7-8, 10".

I solved this task with the following:

let numbers = [1,2,3,4,7,9,12,13];

numbers.sort((a,b) => {return a - b});
let str='';
let startIndex =0, start, end;
if(numbers.length === 1) {
  str = `${numbers[0]}`;
}

for(let i=0; i< numbers.length; i++) {
  if(i === 0) {
    continue;
  }

  if(numbers[i-1] +1 !== numbers[i]) {   
    start = numbers[startIndex];
    end = numbers[i -1];
    if(start - end === 0) {
      str += `${start},`;
    }
    else {
       str += `${start} - ${end},`;
    }

    startIndex = i;

  } 

  if(i+1 === numbers.length) {
    start = numbers[startIndex];
    end = numbers[i];
    if(start - end === 0) {
      str += `${numbers[i]}`;
    } else {
           str += `${numbers[startIndex]} - ${numbers[i]}`;
    }
  }

}

console.log(str);

But, code looks very complex for understanding. Is there a better way to do this?

DEMO

What you want to achieve is not clear. Please try to elaborate more on expected result. — Sachin I
– Sachin I, Commented Dec 21, 2016 at 9:00
@Xufox. This is not about code review only, As I said, may be better way is exist, algorithm for example. — user348173
– user348173, Commented Dec 21, 2016 at 9:03

Nina Scholz · Accepted Answer · 2016-12-21 16:00:20Z

2

You could test the items with their predecessor and move it to the right group.

var data = [1, 2, 3, 5, 7, 8, 10],
    result = data.reduce(function (r, a, i, aa) {
        if (aa[i - 1] === a - 1) {
            r[r.length - 1][1] = a;
        } else {
            r.push([a]);
        }
        return r;
    }, []).map(a => a.join('-')).join(', ');

console.log(result);

edited Dec 21, 2016 at 16:00

answered Dec 21, 2016 at 9:13

Nina Scholz

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1 Comment

user348173 Over a year ago

Excellent solution, Thank your very much, Nina.

georg · Accepted Answer · 2016-12-21 09:16:33Z

2

Here's a function that converts a (sorted) array into an array of pairs (ranges).

let rangify = function(xs) {
    let ranges = [];
  
    for (let x of xs) {
        let last = ranges[ranges.length - 1];
  
        if (!last || x > last[1] + 1)
            ranges.push([x, x])
        else
            last[1]++;
    }
  
    return ranges;
};


let r = rangify([1,2,3,5,7,8,10,11,12,13,77,78]);
console.log(r)

It should be obvious how to get your desired output from that.

answered Dec 21, 2016 at 9:16

georg

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