How to find median/average days between entries (orders) for 50,000 items

[Garuda7]

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[TD]9/1/16[/TD]
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Hello, I was trying to figure out the best way to find the median/average days between entries. So, from the chart above, Item 1 would have an average of 3 days between entries. For Item 2, it would be 11 days. For Item 3, it is more sporadic which would represent more like my actual data. The date row would be for an entire year and the Item column would have more than 50,000 entries. Doing a "=Count over the period" would not be accurate since, say for instance, Item 4 was entered exactly every week for an entire year so it would have 52 entries and an average of 7 days. But, Item 5, was more of a seasonal item that was entered in the fall and spring and had 26 entries respectively; showing 52 entries but an average of 7 days (falsely). I've come across =Subtract, =NetworkDays, =DatedIf functions but haven't come up with a solution. Any help would be great. Thanks!

 

[oldbrewer]

for item 5 you would have to "ignore" gaps of say more than 10 days

 

[oldbrewer]

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[TD="align: right"]01/01/2015[/TD]
[TD="align: right"]08/01/2015[/TD]
[TD="align: right"]15/01/2015[/TD]
[TD="align: right"]22/01/2015[/TD]
[TD="align: right"]29/01/2015[/TD]
[TD="align: right"]01/08/2015[/TD]
[TD="align: right"]09/08/2015[/TD]
[TD="align: right"]17/08/2015[/TD]
[TD="align: right"]25/08/2015[/TD]
[TD="align: right"]02/09/2015[/TD]
[TD="align: right"]10/09/2015[/TD]
[TD="align: right"]18/09/2015[/TD]
[TD="align: right"]26/09/2015[/TD]
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[TD="align: right"]7[/TD]
[TD="align: right"]7[/TD]
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[TD="colspan: 3"]set arbritary ignore value of 15[/TD]
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[TD="align: right"]10[/TD]
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[TD="colspan: 3"]=COUNTIF(A2:M2,"< 15")-1[/TD]
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[TD="align: right"]84[/TD]
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[TD="colspan: 3"]=SUMIF(A2:M2,"< 15")[/TD]
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[TD="colspan: 3"]so average gap = 8.4 days[/TD]
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