Sort a JavaScript array of strings with years inside

Question

Evaluating 2 extremely simple arrays, one sorts ok and the other does not:

var qtr = ['zzqtr_1_2020','zzqtr_2_2020','zzqtr_3_2019','zzqtr_4_2019'];
qtr.sort();
// qtr is now zzqtr_1_2020, zzqtr_2_2020, zzqtr_3_2019, zzqtr_4_2019 (no change)

var fruits = ["a_1_Banana", "a_2_Orange", "a_1_Apple", "a_1_Mango"];  
fruits.sort();
// fruits is now  a_1_Apple, a_1_Banana, a_1_Mango, a_2_Orange (SORTED!)

What I cannot figure out is why the qtr array will not be sort properly?

It is sorting, but it's already in sorted order. What do you expect to be different? — Pointy
– Pointy, Commented Apr 30, 2020 at 17:47
I wonder if he's expecting it to be sorted as a date, so that the 2019 items should go before 2020. — Barmar
– Barmar, Commented Apr 30, 2020 at 17:49
if you like to get the data sorted by date, you could consider to use strings which have the year in front of the month, like an ISO 8601 date string. this is sortable, despite of the same prefix. — Nina Scholz
– Nina Scholz, Commented Apr 30, 2020 at 17:52
@NinaScholz Also need 2-digit months, otherwise 12 will sort before 3 — Barmar
– Barmar, Commented Apr 30, 2020 at 17:54

Radu Diță · Accepted Answer · 2020-04-30 17:47:38Z

2

Because the array is already sorted. Your difference is made by the id after "zzqtr_". And the elements are already sorted.

answered Apr 30, 2020 at 17:47

Radu Diță

14.3k2 gold badges33 silver badges37 bronze badges

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

Comments

TrèsAbhi · Accepted Answer · 2020-04-30 17:50:27Z

0

The array is already sorted. The string after "zzqtr_" are in increasing order (ie: from 1 to 4). So, if you did something like this:

var qtr = ['zzqtr_3_2020','zzqtr_1_2020','zzqtr_4_2019','zzqtr_1_2019'];
qtr.sort();
var x = qtr.toString();

now, you will see a change :)

answered Apr 30, 2020 at 17:50

TrèsAbhi

1052 silver badges10 bronze badges

Comments

Danziger · Accepted Answer · 2020-04-30 17:54:24Z

0

Array.prototype.sort() is comparing UTF-16 sequences, so zzqtr_1, zzqtr_2, zzqtr_3, zzqtr_4 is already sorted according to that, the last bit of text (the year) is not relevant there.

I assume you want to sort by year, so in that case, you need to implement a custom sorting function:

const qtr = ['zzqtr_1_2020','zzqtr_2_2020','zzqtr_3_2019','zzqtr_4_2019'];

qtr.sort((a, b) => {
  const aParts = a.split('_');
  const bParts = b.split('_');
  
  return (parseInt(aParts[2]) - parseInt(bParts[2])) || a.localeCompare(b);
});

console.log(qtr.join(', '));

edited Apr 30, 2020 at 17:54

answered Apr 30, 2020 at 17:48

Danziger

21.4k6 gold badges59 silver badges91 bronze badges

Comments

Faraaz Malak · Accepted Answer · 2020-04-30 19:17:47Z

0

Array.prototype.sort() works by comparing UTF-16 code points, which can lead to unexpected results sometimes.

Instead, consider using String.prototype.localeCompare() function, which compares two strings, based on the alphabets of the locale and not UTF-16 code points

answered Apr 30, 2020 at 19:17

Faraaz Malak

3391 silver badge6 bronze badges

Collectives™ on Stack Overflow

Sort a JavaScript array of strings with years inside

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related