One to many relationship to fetch values in an alternate rows - excel

Question

I am trying to fetch dates from sheet1 with common ID (there are multiple occurrences in sheet1) using an array formula in a cell (then dragging it to the right side to have all the dates belong to specific ID):
=IF(COLUMNS($E2:E2)<=$D2,INDEX(Sheet1!$B$2:$B$13,SMALL(IF(Sheet1!$A$2:$A$13=Sheet2!$A2,
ROW(Sheet1!$A$2:$A$13)-ROW(Sheet1!$A$2)+1),COLUMNS($E2:E2))),"")
But, whenever I try to insert one column (for counting purposes) in b/w the columns, this formula doesn't work. I can't figure out the issue, would really appreciate the help?
Thank you.

Answer 1

Assuming that your first formula is in E2, and that the cells in row 2 of any newly-inserted columns will always be blank, replace the two instances of:
COLUMNS($E2:E2)
in your formula in E2 with:
COUNT(1/LEN($D2:D2))
As a way of explanation, take the formula in F2, for which this part will be:
COUNT(1/LEN($D2:E2))
(The only part having changed naturally being the end range reference.)
And let's assume that 3 new columns are inserted to the left of column E, which means that E2, F2 and G2 will now be blank, H2 will contain the entry which was previously in E2, and, for the formula in I2, the above part will now be:
COUNT(1/LEN($D2:H2))
Clearly we wish this part to continue to give 2, since this cell should still represent the second of our returns.
Using LEN is a rigorous way to determine whether a cell is empty or not. Other functions are also available for this purpose, though may give incorrect results depending upon whether the blanks in that range are "genuine" blanks or the null string "" as a result of formulas in those cells.
If a cell is empty, it has a length of 0. Hence, in this example, the above resolves to:
COUNT(1/{1,0,0,0,2})
(Where I've made some random assumptions about the lengths of the strings in cells D2 and H2.)
There are many ways to determine how many non-zeroes there are in an array. SUMPRODUCT would be one; I chose another, the logic being that the above becomes, after reciprocation with unity:
COUNT({1,#DIV/0!,#DIV/0!,#DIV/0!,0.5})
and, since COUNT ignores any errors in the range passed to it, the above resolves to 2, as desired.
Regards