this.state = {
   board: [
     [null, null, null, null],
     [null, null, null, null],
     [null, null, null, null],
     [null, null, null, null]
   ]
}

// x & y are the coordinates of the 2d array

this.setState({
      board: update(this.state.board, {
        [x]: {
          [y]: { $set: { id, player, x, y, waitingToBeSelected } }
        }
      })
    });

this.state = {
   board: [
     [null, null, null, null],
     [null, {id: 21, player: "p1", waitingToBeSelected: false, x:1, y:1}, null, null],
     [null, {id: 42, player: "p1", waitingToBeSelected: false, x:2, y:1}, null, null],
     [null, null, null, null]
   ]
}