code: function appendJoinRow(arrayCols, keyDf, leftNonKeyDf, rightNonKeyDf,
    leftInd, rightInd, indicatorValue, rightIndForKey) {
  
    var keyInd = rightIndForKey ? rightInd : leftInd;
    var i, nCol;
    var colInd = 0;
    nCol = keyDf.nCol();
    for (i = 0; i < nCol; i++) {
      arrayCols[colInd].push(keyDf._cols[i].values[keyInd]);
      colInd++;
    }
    nCol = leftNonKeyDf.nCol();
    for (i = 0; i < nCol; i++) {
      var leftVal = (leftInd === null) ? null :
        leftNonKeyDf._cols[i].values[leftInd];
      arrayCols[colInd].push(leftVal);
      colInd++;
    }
    nCol = rightNonKeyDf.nCol();
    for (i = 0; i < nCol; i++) {
      var rightVal = (rightInd === null) ? null :
        rightNonKeyDf._cols[i].values[rightInd];
      arrayCols[colInd].push(rightVal);
      colInd++;
    }
    if (colInd < arrayCols.length) {
      // Add the join indicator value if there's a final column for it
      arrayCols[colInd].push(indicatorValue);
    }
  }
docs: Helper for appending values to "arrayCols" from "leftInd" and "rightInd"