using splice inside 2D Array in Javascript

Question

I've created this 2D array, and I'm trying to delete the rows that are having 5 "ones" or more, I tried it with splice (a.splice(j,1)) but it doesn't work . I think because when using this method it changes the whole quantity of rows and that's affects the for loops.

Is it because I don't use splice correctly or should I use different method ?

Thanks !

a = Array(7).fill(0).map(x => Array(10).fill(0))

for (let i = 0; i < 5; i++) {
  a[1][i + 2] = 1;
  a[4][i + 2] = 1;
  a[5][i + 2] = 1;
}

console.log(a);


let count = 0;
for (let j = 0; j < 7; j++) {
  for (let i = 0; i < 10; i++) {
    if (a[j][i] == 1) {
      count = count + 1;
    }
  }
  if (count > 4) {
    console.log("Line" + j);
    // a.splice(j,1);
  }
  count = 0;
  // a.splice(j,1);
}

You can create a new array with filtered values and use it easily. — Rajpal Singh
– Rajpal Singh, Commented Jul 4, 2022 at 8:43

Robin Mackenzie · Accepted Answer · 2022-07-04 10:00:38Z

2

Your splice is correct but you move forward through the array (j is incremented). To do this type of operation you need to move backward through the array (j is decremented) - this way the changing array indices don't intefere with your loop.

See the example below:

a = Array(7).fill(0).map(x => Array(10).fill(0))

for (let i=0; i<5; i++) {
  a[1][i+2] = 1;
  a[4][i+2] = 1;
  a[5][i+2] = 1;
}

console.log("Original array");
console.log(a);

for (let j = a.length - 1; j > 0; j--) {
  var count;
  
  for (let i = 0; i < a[j].length; i++) {
    if (a[j][i] === 1) {
      count += 1
    }
  }
  
  if (count > 4) {
    a.splice(j, 1);
  }
  
  count = 0;
}

console.log("Filtered array");
console.log(a);

answered Jul 4, 2022 at 10:00

Robin Mackenzie

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