Find minimum in array of arrays js

Question

I have an array of arrays, each one of them consists of two values - timestamp and price.

[
  [1147651200000, 376.2],
  [1147737600000, 350],
  [1147824000000, 374.5]
]

I need to find date and time in which price was the lowest among all points. What function should I use, pls help.

EDIT:

Thanks everyone! I took tests to to see which function is fastest. Here is how I did it (example with .sort, others are same)

console.time('cycle');
var k = 0;
while (k<10000) {
var input = [
  [1147651200000, 376.2],
  [1147737600000, 350],
  [1147824000000, 374.5]
];

var output = input.sort(function(a,b){
  return a[1] > b[1];
})[0];
k++;
}
console.log(output);
console.timeEnd('cycle'); //36 ms

.map //67 ms
minimum in cycle // 108 ms

Use .sort with a custom callback to sort by the price value, then get the first element of the resulting array. This will be the one with the lowest price. — Niet the Dark Absol
– Niet the Dark Absol, Commented May 29, 2014 at 12:24
The underscore library has a min function that can achieve this easily, var min = _.min( input_array, function(n){ return n[1]; }); — scragar
– scragar, Commented May 29, 2014 at 12:27
Nope. That's not what StackOverflow is for :p Search around, give it a try, and if you have problems then come back with some code ;) — Niet the Dark Absol
– Niet the Dark Absol, Commented May 29, 2014 at 12:27

hsz · Accepted Answer · 2014-05-29 12:27:48Z

5

Just try with:

var input = [
  [1147651200000, 376.2],
  [1147737600000, 350],
  [1147824000000, 374.5]
];

var output = input.sort(function(a,b){
  return a[1] > b[1];
})[0];

Output:

[1147737600000, 350]

answered May 29, 2014 at 12:27

hsz

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6 Comments

Spencer Wieczorek Over a year ago

Nothing wrong with this solution, just want to point out in case you have a huge amount of elements. You can find the lowest item in O(n) other than quick-sort using O(n log n).

Prosto Trader Over a year ago

@SpencerWieczorek, I do have huge amount of elements. But i did'n get you answer. Can you clarify pls what function should look like?

RichieHindle Over a year ago

@ProstoTrader: I've posted an O(N) answer.

Spencer Wieczorek Over a year ago

@ProstoTrader: As RichieHindle pointed out, there are a few O(n) solutions below. So I don't need to post an answer that they already have done.

Spencer Wieczorek Over a year ago

@ProstoTrader .sort() is not faster. Again it's O(n) vs O(n log n), you are only testing for a 3 element array. With a few thousand elements you will see that O(n) is faster. For example n = 3 : n log n = 1.431 vs n = 3. But n = 1000 : n log n = 3000 vs n = 1000. These are not opinions.

|

RichieHindle · Accepted Answer · 2014-05-29 12:31:24Z

2

Sorting the array is O(N logN) - if performance with large arrays might be an issue, here's an O(N) solution:

var min = a[0];
for (var i = 1; i < a.length; i++) {
    if (a[i][1] < min[1]) {
        min = a[i];
    }
}

// min is now [1147737600000, 350]

answered May 29, 2014 at 12:31

RichieHindle

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Comments

adeneo · Accepted Answer · 2014-05-29 12:31:03Z

1

Get the numbers from the array into a new array, use Math.min to get the lowest, and backtrack to get the timestamp.

var arr = [
  [1147651200000, 376.2],
  [1147737600000, 350],
  [1147824000000, 374.5]
] 

var numbs     = arr.map(function(x) { return x[1]||0 });
var timestamp = arr[numbs.indexOf(Math.min.apply( Math, numbs ))][0];

FIDDLE

answered May 29, 2014 at 12:31

adeneo

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5 Comments

adeneo Over a year ago

@ProstoTrader - Array.sort would by far be the slowest way to do this, if you can prove otherwise, show us.

RichieHindle Over a year ago

@adeneo: Thanks for putting together those tests! You should post the reverse-for example as an answer.

Prosto Trader Over a year ago

@adeneo, look at the edit, it shows, how I did tests. I moght be wrong but minimum time has sort.

RichieHindle Over a year ago

@ProstoTrader: You timed how long it took to find the minimum of three items, ten thousand times. In your comment you said "I do have huge amount of elements." It would make more sense to time how long it takes with a huge amount of elements, not how long it takes with three. adeneo's tests time it with a thousand elements.

Prosto Trader Over a year ago

OK I got it. I think you are right, I've just tried to make quick tests in console.

RazvanDH · Accepted Answer · 2014-05-29 12:31:27Z

0

Maybe something like this?

var min = arr[0][1];
var timestamp = 0;
for(i in arr) {
    if(arr[i][1] <= min ) {
        min = arr[i][1];
        timestamp = arr[i][0];
    }
}

answered May 29, 2014 at 12:31

RazvanDH

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