Populate specific array indices from other array in JavaScript

Question

I have 2 arrays, arr1 and arr2. They're both 2-dimensional. I want to copy certain array values from arr1 to arr2.

For instance, I want to copy the value from arr1[9][9] into arr2[0][0]. My guess was to write arr2[0][0] = arr1[9][9]; but that failed.

I looked at some similar questions on this site but they did not answer my question.

Here is the code for the particular situation. The code is written is Google Apps script.

  // eplList and attList are both arrays. They are filled below (I checked, the values exist)
  var eplList = epl.getRange(2, 2, eplLastRow, 2).getValues();
  var attList = attsheet.getRange(3, 1, attLastRow, 20).getValues();

  var eplListLength = eplList.filter(String).length;
  var attListLength = attList.filter(String).length;

  // Declaring the empty array I want to fill
  var masterArray = [];

  var ix, jx, day;

  // Here I begin to fill the array
  for (ix = 0; ix < eplListLength; ix++)
  {
    masterArray[ix][0] = eplList[ix][0]; // This is where I am getting the error message 
    masterArray[ix][1] = eplList[ix][1];

      for (jx = 0; jx < attListLength; jx++)
      {
        if (eplList[ix][0] == attList[jx][day*4-4])
          masterArray[ix][6+day] = masterArray[ix][6+day].concat(" ", attList[jx][day*4-2], ": ",attList[jx][day*4-3]);
      };
 // and some morecode
  };

The error I'm getting is "TypeError: Cannot set property '0' of undefined"

You need to initialize the inner array: masterArray[ix] = [] in the for loop. Also, the variable day is never set a value — adiga
– adiga, Commented Apr 9, 2021 at 8:23
@user256872 where? You need to initialize the each inner array. for (ix = 0; ix < eplListLength; ix++) { masterArray[ix] = []; <-- here — adiga
– adiga, Commented Apr 9, 2021 at 8:25

Oleksandr Sakun · Accepted Answer · 2021-04-09 08:30:02Z

1

To fix particular issue you've got try this code, but i not sure about code below):

masterArray[ix] = [eplList[ix][0], eplList[ix][1]]; // This is where I am getting the error message

answered Apr 9, 2021 at 8:30

Oleksandr Sakun

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5 Comments

Oleksandr Sakun Over a year ago

So, you do not need this line at all: masterArray[ix][1] = eplList[ix][1];

Oleksandr Sakun Over a year ago

No problem, what about code below (nested for). Did it fail?

user256872 Over a year ago

so far so good, it's still in development :)

adiga Over a year ago

@user256872 you need to set the value of day somewhere. It's undefined and 6 + day will return NaN

user256872 Over a year ago

yes I have it set in my code I just accidentally removed it here. thank you

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