troubleshooting Question

Understanding a few parts of an array-entered formula in Excel

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WeThotUWasAToad asked on
Microsoft OfficeMicrosoft Excel
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Hello,

Can someone provide an explanation for a couple of parts of the array-entered Excel formula described below?

I've been tinkering with an array formula for several days, trying to understand how it does what it does as the solution to the thread located here:
        Extract certain items from one list to create another list in Excel

A shortened version (10 rows instead of 20 rows) of the formula is:
{=IFERROR(INDEX(B$1:B$13,SMALL(IF((C$4:C$13=F$2)*ROW(C$4:C$13)=0,1E+38,(C$4:C$13=F$2)*ROW(C$4:C$13)),ROWS($4:4))),"")}
The purpose of the formula is depicted in the following screenshot where its function is to create an ordered list (in column F) of the names in column B which have an adjacent letter in column C that matches a manually-entered letter in the box at cell F2. (By the way, column E contains a formula which displays numbering only if the adjacent column-F cell is not blank — see footnote *a).

2017-11-04a.png        (Note: all screenshots in this post are taken from the attached Excel file.)

The formula works great but I really want to understand each part of what it's doing because I have several other places where it would be useful. So working from the inside out, I looked at the cell-display results of various segments when they are entered 1) as standard formulas and 2) when they are entered as array formulas (Ctrl+Shift+Enter).

I also used a trick I learned a couple of years ago which enables you to 3) see the complete results of a formula by selecting the formula in the Formula Bar then pressing F9 (see footnote *b).

The following screenshot shows these three results for several segments of the formula:

        • #1 & #2 are shown in column F and
        • #3 (the F9 result), is pasted with a black font in column H:

2017-11-04b.png
By the way, cells with red italics use the Excel4 function =GET.CELL(6, [ref]) to display the formula residing two cells to the left (eg H40 shows the formula in F40) (see footnote *c).

The next thing I did was to transpose the F9 results into a table with heading numbers corresponding to the evaluated segments and wrote down definitions/explanations (blue font) of what I think is happening. These steps are shown in the next two screenshots:

2017-11-04e.png
2017-11-04f.png
I think I understand most of the process up through item #7 and I'm fairly familiar with the INDEX() & IFERROR() functions (in #11 & #12). But I have not previously used the ROWS() or SMALL() functions — although I've read about them and gone through some examples and they seem to be quite straightforward.

I suspect the biggest hurdle is understanding how to get from essentially evaluating each original-data row one-at-a-time to get an array of 10 results at each step (if that's the correct terminology) to having the three names (Abigail, Hannah, & Sophia) which are "still standing" after all the steps (ie do not get assigned the huge number in #7), compiled into the final list of three names.

Maybe if someone could respond with how you would edit/fill-in the blue-font descriptions for #8, #9, & #10, that would do the trick. Other similar examples are always helpful as well.

Thanks, Steve
__________________________________________________

Footnotes:

*a — The formula in column E is:

        =IFERROR(IF(OFFSET(E4,0,1)<>"",OFFSET(E4,-1,0)+1,""),"")

pasted down to row 13.

*b — I got the F9 tip from Rory Archibald about two years ago and here is the Microsoft doc on the same topic.

Also, Ctrl+z undoes the function (if you remember to do it before leaving the Formula Bar).

*c — Here is a link I found with some information about Excel4 functions. I'm interested in finding other/better references on this topic in case anyone knows of one.

By the way, the:

        =GET.CELL(6, [ref])

function does not, for some reason, display curly brackets when an array formula is present, so I manipulated it a bit to make it work in those cases:

        ="{"&GET.CELL(6,AutoFilter!H16)&"}"

This is shown in the Name Manager where I named the standard function "Formula" and the manipulated form "ArrayFormula" as shown in the next two screenshots:

2017-11-04c.png
2017-11-04d.png
File: AutoFilter-array-formula-evaluation.xlsm
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