Forum Discussion
Including 0 values when calculating STDEV
Hi epicleo,
As the GilbertQ said, if all they are null where sales are zero, you can change it by calculating a calculated column using the formula.
New Column=IF(ISBALNK(Table[column]),0,Table[column])
Then use the new column in your 26-W.STDEV formula, and check if it works fine.
Best Regards,
Angelia
Sorry for the delay. There is actually no value. Let me walk you through a better example. I am attempting to determine the most recent 6-Month STDEV for sales by product in order to determine variation.
The Sales Datais made up of daily transactions so it contains a iContractsChargebacks[TransactionDate] and iContractsChargebacks[ChargebackUnits] (i.e. sales), but if there are no sales in a given month, then there will be no data for that month.
So, for example, on July 1st, sales for the past 6 months were the following:
Jan 100
Feb 125
Apr 140
May 125
Jun 130
March is missing because there were no sales. So, when I calculate STDEV on the data set, it is calculating it over 5 periods, when in fact there were 6, just one happend to be zero.
The code I am curretly using is:
6M STDEV = CALCULATE(
STDEVX.P(
VALUES(DimDate[Calendar Month Number]),
CALCULATE(SUM(iContractsChargebacks[ChargebackUnits]))
),
FILTER(ALL(DimDate),
DimDate[Month ID]<=MAX(DimDate[Month ID])-1 &&
DimDate[Month ID]>=MAX(DimDate[Month ID])-6
))
Instead of using date parameters in the code, I created a calculated column in the date table that gives each Month a unique ID, makes it easier for me.
What I need the formula to do is calculate STDEV across the six month period. If when pulling the monthly sales numbers, it only comes back with 3 periods, then it needs to assume the other 2 periods with a zero value.
Thank you for your help with this!!
Hi epicleo
What I would suggest doing is rather than to try and figure out when there is no data I would solve it by doing the following.I would left join from your DimDate table, to your Fact (Source Data) table. By doing a left join from the DimDate table it will then bring in all the dates. This will then allow your data to be blank when there is no data.
Then based on your requirements you can then use the same measures and not it should show zero for the months where there is no data when you put in your Date column from your DimDate table.
GilbertQ Thank you for the help; that would be a great work around except that I m dealing with more than 1000 SKUs so my query would produce a few million rows given we transact on a daily basis and are reporting on 3 to 5 year period.
I thought about manaully calculating standard deviation instead of using the DAX STDEVX.P formula and found these 2 as a reference on how to do so, the first being closest to my need:
https://community.powerbi.com/t5/Desktop/Problem-with-STDEV/td-p/19731
So, given my detail above, I attempted to make a go of it, but still am not getting the correct number. My code is:
STDEVX2 =
var Averageprice=[6M Sales]
var months=6
return
SQRT(
DIVIDE(SUMX(
FILTER(ALL(DimDate),
DimDate[Month ID]<=(MAX(DimDate[Month ID])-1) &&
DimDate[Month ID]>=(MAX(DimDate[Month ID])-6)
),
(iContractsChargebacks[SumOfOrderQuantity]-Averageprice)^2),
months
)
)I am determined to figure this out and I appreciate all your help with this. Thank you in advance!!!
What I would suggest doing is if you can just get a dataset for the months that you are testing, and by using the merge to see it can get to the number you are expecting to be the result?
This should then ensure that the theory is correct. Which is important to know that you can calculate the final number.
Then if the above works, if you had to bring in all the data, how large would the data model be? As there are always ways to optimize the data model. And I have worked with large datasets with a few million rows and it has still been very fast both when developing as well as once deployed to the Power BI Service.
