Calculating average time between transactions + stdev for each customer

[#1]

Hi guys,

Would you please suggest me a method to calculate average  number of days between transactions (+ standard deviation) for my customers.

Here is the dataset (column datedifD is added just for information and is not actually present in datamodel):

custID	transID	transDate	transValue	datedifD
1	1	10.03.2012	50
1	2	24.03.2012	20	14
1	3	29.03.2012	10	5
1	4	12.04.2012	90	14
1	5	05.05.2012	90	23
1	6	09.05.2012	90	4
1	7	01.06.2012	90	23
1	8	26.06.2012	80	25
1	9	29.06.2012	100	3
1	10	16.07.2012	90	17
1	11	17.07.2012	20	1
1	12	06.08.2012	60	20
1	13	14.08.2012	50	8
1	14	11.09.2012	90	28
1	15	23.09.2012	70	12
2	1	22.08.2012	30
2	2	01.09.2012	10	10
2	3	08.09.2012	20	7
2	4	30.09.2012	20	22
2	5	23.10.2012	30	23
2	6	01.11.2012	100	9
2	7	17.11.2012	30	16
2	8	22.11.2012	70	5
3	1	19.02.2010	50
3	2	07.03.2010	100	16
3	3	02.04.2010	40	26
3	4	22.04.2010	50	20
3	5	11.05.2010	50	19
4	1	03.01.2012	100
4	2	11.01.2012	100	8
4	3	14.01.2012	40	3
4	4	04.02.2012	50	21
4	5	08.02.2012	40	4
4	6	14.02.2012	90	6
4	7	15.02.2012	90	1
4	8	18.02.2012	90	3
4	9	07.03.2012	30	18
4	10	24.03.2012	20	17
4	11	14.04.2012	40	21
4	12	01.05.2012	20	17
4	13	04.05.2012	90	3
4	14	21.05.2012	10	17
4	15	05.06.2012	80	15
4	16	04.07.2012	10	29
4	17	17.07.2012	100	13
4	18	12.08.2012	20	26
4	19	02.09.2012	90	21
4	20	08.09.2012	20	6
4	21	01.10.2012	20	23
5	1	04.02.2011	50
5	2	17.02.2011	80	13
5	3	04.03.2011	90	15
5	4	20.03.2011	10	16
5	5	09.04.2011	30	20
5	6	01.05.2011	10	22
5	7	12.05.2011	60	11
5	8	17.05.2011	70	5
5	9	24.05.2011	50	7
5	10	02.06.2011	90	9
5	11	21.06.2011	100	19
5	12	17.07.2011	40	26
5	13	08.08.2011	50	22
5	14	22.08.2011	80	14
5	15	06.09.2011	10	15

And here is the desired output

custID	average time (d) between transactions	standard deviation
1	14.07	8.92
2	13.14	7.24
3	20.25	4.19
4	13.60	8.69
5	15.29	6.08

Thanks a lot in advance

Dmitry

P.S. Forgot to mention, the data already loaded. I cannot make changes in the load script.

Message was edited by: excelgod

[Anonymous]

Here you go:

LOAD custID,

     avg(datedifD) as datediffAvg

FROM

transactions.xls

(biff, embedded labels, table is values$)

group by custID;

[#3]

Thanks for reply. I cannot change loading scripts. I should only play with formylas in charts + datedifD is not present in QV, I showed it for information only.

[swuehl]

You can create a straight table with dimension custID and as expression:

=(max(transDate)-min(transDate)) / (max(transID)-1)

[#5]

Wow.Thanks.What an elegant solution.It really solves the problem with the mean...

I also need the standard deviation (didn't put it to keep example simpler, my mistake). Here I absolutely need to calculate difference between dates of consecutive transactions, and later to calculate stdev for these differences.

[swuehl · Accepted solution]

Instead of above expression, you could also use

=avg(aggr( transDate -above(transDate),custID,transID))

[NOTE: to get correct results, the load order of transID must be ascending, i.e. your records mustn't come in all mixed up. In your sample data, that looks ok to me]

Then the standard deviation could just be

=stdev(aggr( transDate -above(transDate),custID,transID))

[#7]

thanks I'll check immediately

[#8]

you are supeman. works perfectly

[#9]

is there a way to sort transaction date on the fly (in the formula) in case there is no order or the order is not suitable?

[swuehl]

Unfortunately, you can't define a sort order in the advanced aggregation function aggr(). I believe it will always use the load order for sorting its dimension values.