JS subset of array of arrays

Question

If I have an array of arrays as follows:

[ [ A0 , B0 , C0 , D0 , E0 ],
  [ A1 , B1 , C1 , D1 , E1 ],
  [ A2 , B2 , C2 , D2 , E2 ]  ] // array of 3x5

and I want to get a new array of subset arrays like so:

[ [ A0 , B0 , C0           ],
  [      B1 , C1 , D1      ],
  [           C2 , D2 , E2 ]  ]  //array of 3x3

This means that the sliceLength = 3, but how can one do this? Is it better to use splice (as in duplicate the original, then remove the unwanted parts), slice, and/or push?

This is what I have thus far, but the syntax looks off:

var newMega = [];
var sliceLength = 3;
for (var i=0; i<originalMatrix.length; i++) {
  var inner = originalMatrix.slice(i, sliceLength);  //  Here is the issue
  newMega.push(inner); 
}

It appears that the syntax would call slice on the entire originalMatrix, without knowing which index of the nested arrays it should be slicing. Should it be originalMatrix[i].slice(i, sliceLength) ?

Answer 1

Try slicing the inner array ( originalMatrix[i] ). Also, you probably want to call splice rather than slice :

var newMega = [];
var spliceLength = 3;
for (var i=0; i<originalMatrix.length; i++) {
  var inner = originalMatrix[i].splice(i, spliceLength);
  newMega.push(inner); 
}

Here's a demonstration .