How can I sort a list of lists by order of the last element?

Here is my best attempt so far:

var mylist = [ [1, 'c'], [3, 'a'],  [5, 'b']];
mylist.sort(function(a,b){return a[1]-b[1];});

My call to sort has not effect, and mylist remains in the same order.

How can I sort a list of lists by order of the last element?

Here is my best attempt so far:

var mylist = [ [1, 'c'], [3, 'a'],  [5, 'b']];
mylist.sort(function(a,b){return a[1]-b[1];});

My call to sort has not effect, and mylist remains in the same order.

• javascript
• sorting

• 1 use > or < instead of - – juvian Commented Jan 4, 2016 at 20:31

2 Answers 2

var mylist = [ [1, 'c'], [3, 'a'],  [5, 'b']];
mylist.sort(function(a,b){return a[1].localeCompare(b[1]);});
console.log(mylist)

Use a[1].localeCompare(b[1]) to sort the list in the ascending order or b[1].localeCompare(a[1]) for other way round. This way you will be comparing two strings. You were trying to subtract one string from the other which return NaN.

var mylist = [ [1, 'c'], [3, 'a'],  [5, 'b']];

// to sort by 1st NUMBER element; minus also used for object such as date 
mylist.sort(function(a,b){return a[0] - b[0];}); 

// to sort by 2nd STRING element with >. 
// strings can be compared based on alphabetical order with > or <, 
// but not with a math order operator -, which is supposed to used for comparison between number or date.
mylist.sort(function(a,b){return a[1] > b[1];}); 

Above mentioned examples gives sorting in ascending order, here I note what I understand for who may need: to sort in ascending order [1,9,7] to [9,7,1], we could image there is an empty array[], then we'll just put each element one by one to this array in the right order (based on comparison with existing elements).

function(a,b) { return b - a; }

here a is existing one, b is the one we are going to put in the array.

• if return > 0 (true) >> [b,a] , we could consider the return value as the order of a, positive/true means a should put later, that's the sort() means.
• if return <=0 (false) >> [a,b]

for [1,9,7], the loop will be:

[]

// to put 1
[1]

// to put 9
a = 1, b = 9, b - a > 0 ==> [9,1]

// to put 7
a = 9, b = 7, b - a < 0 ==> [9,7,1]

a = 1, b = 7, b - a > 0 ==> [9,7,1]