Average Data for 15 min Intervals with Different Number of Data For Some Intervals

Hope someone can help me, I don't have much experience in coding.

I want to average the given flows into 15 min intervals. I have data once every minute for most of the 15 min interval, but not all. I am sure there is some type of formula/coding to show this data, but I cannot figure it out. Here is an example:

Date/Time[INDENT] GPM[INDENT] Date/Time 15min Intervals[INDENT] Average GPM
4/12/2017 1:00[INDENT] 100[INDENT] 4/12/2017 1:00[INDENT] 102.67
4/12/2017 1:04[INDENT] 102[INDENT] 4/12/2017 1:15[INDENT] 90
4/12/2017 1:14[INDENT] 106[INDENT] 4/12/2017 1:30[INDENT] 125
4/12/2017 1:15[INDENT] 95
4/12/2017 1:17[INDENT] 105
4/12/2017 1:23[INDENT] 75
4/12/2017 1:28[INDENT] 85
4/12/2017 1:33[INDENT] 120
4/12/2017 1:36[INDENT] 130

I need to know how to figure out the fourth column shown for a very large excel file.

Try this:

=AVERAGEIFS(C:C,B:B,">="&E2,B:B,"<"&(E2+0.25/24))

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 two helper columns for the lower and upper row interval boundaries.

In column C

Formula:

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In column D

Formula:

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In column E the averages @ 15 min intervals or the last interval < 15 min.

Formula:

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Try this array formula:

=IFERROR(AVERAGE(IF(MOD($A$2:$A$29,1)>=D2,IF(MOD($A$2:$A$29,1)<(D2+0.25/24),$B$2:$B$29))),"")

Array Formulae are a little different from ordinary formulae in that they MUST be confirmed in the FIRST CELL ONLY by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER. After that, the array can be dragged down as normal, to cover the desired range.

You will know the array is active when you see curly brackets { } - or "curly braces" for those of you in the USA, or "flower brackets" for those of you in India - appear around the outside of your formula. If you do not use CTRL+SHIFT+ENTER you will (almost always) get an error message or an incorrect answer. Press F2 on that cell and try again.

Don't type the curly brackets yourself - it won't work...

You're welcome and thanks for the rep.