Trouble with conditional LINEST function

Example file attached (I think)

Will you please attach a SMALL sample Excel workbook (10-20 rows of data is usually enough)? Please don't attach a picture of one (no-one will want to re-type all your stuff before starting).

1. Make sure that your sample data are truly REPRESENTATIVE of your real data. The use of unrepresentative data is very frustrating and can lead to long delays in reaching a solution.

2. Make sure that your desired solution is also shown (mock up the results manually).

3. Make sure that all confidential information is removed first!!

4. Try to avoid using merged cells. They cause lots of problems!

Unfortunately the attachment icon doesn't work at the moment. So, to attach an Excel file you have to do the following: Just before posting, scroll down to Go Advanced and then scroll down to Manage Attachments. Now follow the instructions at the top of that screen.

Try this version

=INDEX(LINEST(INDEX(B2:B60,N(IF(1,MODE.MULT(IF((A2:A60="Site2")*(D2:D60="Pre"),(ROW(B2:B60)-ROW(B2)+1)*{1,1}))))),INDEX(E2:E60,N(IF(1,MODE.MULT(IF((A2:A60="Site2")*(D2:D60="Pre"),(ROW(B2:B60)-ROW(B2)+1)*{1,1})))))^{1,2}),1)

confirmed with CTRL+SHIFT+ENTER

change conditions as required

When you use a conditional IF like this:

=IF((A2:A60="Site2")*(D2:D60="Pre"),B2:B60)

.....then you get the required values in the returned array....but also a bunch of FALSE values on rows where the conditions aren't satisfied.

For many functions, like SUM, AVERAGE or MEDIAN, for instance, that's not a problem because the Boolean values are simply ignored....but LINEST doesn't ignore Booleans or blanks so we need a way to return an array which only contains the required values.

To do that we can use this formula:

=INDEX(B2:B60,N(IF(1,MODE.MULT(IF((A2:A60="Site2")*(D2:D60="Pre"),(ROW(B2:B60)-ROW(B2)+1)*{1,1})))))

The IF function returns all the relative row values for the rows where the conditions are satisfied....and also some FALSE values, so with your data this part...

=IF((A2:A60="Site2")*(D2:D60="Pre"),(ROW(B2:B60)-ROW(B2)+1))

will result in this array:

Formula:

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....and we know that if we feed an array like that to MODE.MULT function then the result will be just the numbers without the Booleans..........but only for numbers that appear more than once, hence the {1,1} part which doubles up the above to give this array:

Formula:

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Now because each of the relative row numbers appear twice MODE.MULT will return them all as the most common modal values, i.e. this array:

{35;36;37;38;39;40;41;42;43;44;45;46;47;48;49;50;51;52;53;54;55;56;57;58}

We now want to feed that to INDEX function to get an array of the actual values from row B.....but INDEX is resistant to that, so you need this slightly convoluted setup to do that successfully

=INDEX(B2:B60,N(IF(1,array)))

so the result is just the numeric values from the required rows

This technique is courtesy of XOR LX, see an explanation here