filtering 2d arrays using javascript

Question

I have a 2D array where I need to filter the rows having date field (3d column)

var data = [
['1','a','12-12-2019','A'],
['2','b','','A'],
['3','c','12-1-2019','A'],
['4','d','','A'],
];

The expected result is

result = [
['1','a','12-12-2019','A'],
['3','c','12-1-2019','A'],
];

Using for loop for comprisons is time intensive, Is there a fastest way to retrieve?

for loop will be fastest when it comes to speed, and you should also add on what basis you're filtering data ? — Code Maniac, Apr 13 '19 at 14:30
The basis is existance of date field, as already mentioned in question 3rd column — Code Guy, Apr 13 '19 at 14:32
@CodeGuy added an [answer](https://stackoverflow.com/a/55666633/9624435) with simple for loop you can check — Code Maniac, Apr 13 '19 at 14:38

tkore · Answer 1 · 2021-11-14T00:55:27.437

I wouldn't worry about using a loop to do that - this is what loops are for.

You could just use Array.prototype.filter() to make sure that there's a value in the 2nd position of each array, returning whether it's truthy or not.

var data = [
  ['1','a','12-12-2019','A'],
  ['2','b','','A'],
  ['3','c','12-1-2019','A'],
  ['4','d','','A'],
];

// You're using a Google Apps script, so this is ES5
const result = data.filter(function(item) {
  return item[2];
});

console.log(result);

score 4 · Answer 2 · answered Apr 13 '19 at 14:47

It seems pretty straightforward to just use Array.filter, checking to see if the date field is empty or not.

var data = [
['1','a','12-12-2019','A'],
['2','b','','A'],
['3','c','12-1-2019','A'],
['4','d','','A'],
];

var filtered = data.filter(e => e[2]);

console.log(filtered);

Pranav C Balan · Answer 3 · 2019-04-13T14:41:57.703

Use Array#filter method with Array#some method.

var data = [
  ['1', 'a', '12-12-2019', 'A'],
  ['2', 'b', '', 'A'],
  ['3', 'c', '12-1-2019', 'A'],
  ['4', 'd', '', 'A'],
];

// check any of the string matched date pattern
let res = data.filter(arr => arr.some(str => /^\d{1,2}-\d{1,2}-\d{4}$/.test(str)))

console.log(res)

For the older browser, you can just do it with Array#filter method.

var data = [
  ['1', 'a', '12-12-2019', 'A'],
  ['2', 'b', '', 'A'],
  ['3', 'c', '12-1-2019', 'A'],
  ['4', 'd', '', 'A'],
];


var res = data.filter(function(arr) {
  // check length of date formated elements
  return arr.filter(function(str) {
    return /^\d{1,2}-\d{1,2}-\d{4}$/.test(str)
  }).length;
});

console.log(res)

If you just want to check the 3rd element always then there isn't any need of the nested loop.

var data = [
  ['1', 'a', '12-12-2019', 'A'],
  ['2', 'b', '', 'A'],
  ['3', 'c', '12-1-2019', 'A'],
  ['4', 'd', '', 'A'],
];


var res = data.filter(function(arr) {
  // check 3rd value is correct date value
  return /^\d{1,2}-\d{1,2}-\d{4}$/.test(arr[0])
  // if value would be empty all other case then simply 
  // return the value since empty values are falsy
  // return arr[2];
});

console.log(res)

I am actually using this for an Google apps script, so I cant use => operator — Code Guy, Apr 13 '19 at 14:33
@CodeGuy, all of that should be mentioned in your question. We should not have to read those requirements in comments. — trincot, Apr 13 '19 at 14:34

score 1 · Answer 4 · answered Apr 13 '19 at 14:34

1

When it comes to speed for loop is fastest as your value to match is always at fixed index so you can just directly check and value and push your data

var data = [['1','a','12-12-2019','A'],['2','b','','A'],['3','c','12-1-2019','A'],['4','d','','A'],];

let op = []

for(let i=0; i<data.length; i++){
  if(!data[i][2]){
    op.push(data[i])
  }
}

console.log(op)

answered Apr 13 '19 at 14:34

Code Maniac

37,143
5
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60

You certain a `while` loop isn't fastest? – charlietfl Apr 13 '19 at 14:41
or array.filter? – James Apr 13 '19 at 14:44
@charlietfl well that depends implementations and i have seen some answers [here](https://stackoverflow.com/questions/3629174/which-loop-is-faster-while-or-for) in most of answers it says so, – Code Maniac Apr 13 '19 at 14:44
Just throwing it out there. Hard to know without a perf test. – charlietfl Apr 13 '19 at 14:48

score 1 · Answer 5 · answered Apr 13 '19 at 14:41

var data = [
['1','a','12-12-2019','A'],
['2','b','','A'],
['3','c','12-1-2019','A'],
['4','d','','A'],
];

d = data.filter(i => i[2].match(/\d\d?\-\d\d?\-\d{4}/))
console.log(d)

If you really care the time, then use c++, c, rust or anything, btw, JS is the fastest interpreted language.

filtering 2d arrays using javascript

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