PowerBI calculation using column values separated by 7 days

[Anonymous]

Hi,

I have scoured through the forums here but none of the solutions I have come across work for my case. I'd really appreciate any and all the help I can get as I am fairly new to PowerBI.

I'd like to generate the third and fourth columns in the table below (the 4th column's name is the Excel formula I'd like to implement in PowerBI):

Date		NewObs		Obs7DaysPrior		LOG((NewObs/Obs7DaysPrior),2)
5/6/2020		67
5/7/2020		68
5/8/2020		69
5/9/2020		70
5/10/2020		71
5/11/2020		72
5/12/2020		80		67		0.255838904
5/13/2020		87		68		0.355480655
5/14/2020		87		69		0.334419039
5/15/2020		87		70		0.313660479
5/16/2020		87		71		0.293196376
5/17/2020		90		72		0.321928095
5/18/2020		90		80		0.169925001
5/19/2020		93		87		0.096215315
5/20/2020		95		87		0.126912112
5/21/2020		95		87		0.126912112
5/22/2020		95		87		0.126912112
5/23/2020		97		90		0.108059746

In the above calculation, the difference is 7 days, but it could be 14 or 30 or 5, depending on the requirements in future.

Thanks much,

Cobe.

[lbendlin · Accepted solution]

A couple comments:

Your example talks about 7 days prior but it actually shows 6 days prior.

Are you sure you want logarithm dualis?

Did you mean columns when you wrote columns?

Here's the approach according to your example.

LogN table in Power Query:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("lZFLDoMwDESvUrGuwJ/Y8ZwFcf9rNJUawEAWXVjK4j05nlnXyRZfhISm9/Rq4/X3OGZ7f6maqBhQkSgMKJypSgOKKWE8wjhhMsLkjMXtXprFLDRApRuajA7ut9OsZiXIzbpRng0chpbCIEU37NHYM2kGqzuVuhv+bPBxB5ThWr0bqTrckmo7hCFB2O+IRyOOX7EDYkTcjVQp9Po9mgkubMp9h6R22+qbweJgYZZu8N+G/G2kzlGvETSDggy1tHS3Dw==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, #" " = _t, NewObs = _t, #" .1" = _t, #" Obs7DaysPrior " = _t, #" .2" = _t, #"LOG((NewObs/Obs7DaysPrior),2)" = _t]),
    #"Removed Other Columns" = Table.SelectColumns(Source,{"Date", "NewObs"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Removed Other Columns",{{"Date", type date}, {"NewObs", type number}})
in
    #"Changed Type"

Calculated Columns (!)

Obs7DaysPrior = 
var d = LogN[Date]
return CALCULATE(sum(LogN[NewObs]),all(LogN),LogN[Date]=d-6)

LogN = LOG(divide(LogN[NewObs],LogN[Obs7DaysPrior]),2)

And the result

[Anonymous]

Thanks for responding! The 7 days is just a placeholder as I indicated in my request. Feel free to use 6 if you'd like.

Yes, I'd like to use log(base 2) for the calculations.

I'm not sure about your question: "Did you mean columns when you wrote columns?" but yes, the four columns presented in the table. The first two are the available data and the last two are what I would like to calculate.

Could you help me walk through your LogN PowerQuery? It's completely new to me. Specifically, I'd like to understand how I can incorporate these pieces of code into my workbook:

Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("lZFLDoMwDESvUrGuwJ/Y8ZwFcf9rNJUawEAWXVjK4j05nlnXyRZfhISm9/Rq4/X3OGZ7f6maqBhQkSgMKJypSgOKKWE8wjhhMsLkjMXtXprFLDRApRuajA7ut9OsZiXIzbpRng0chpbCIEU37NHYM2kGqzuVuhv+bPBxB5ThWr0bqTrckmo7hCFB2O+IRyOOX7EDYkTcjVQp9Po9mgkubMp9h6R22+qbweJgYZZu8N+G/G2kzlGvETSDggy1tHS3Dw==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true])

and:

in type table [Date = _t, #" " = _t, NewObs = _t, #" .1" = _t, #" Obs7DaysPrior " = _t, #" .2" = _t, #"LOG((NewObs/Obs7DaysPrior),2)" = _t]),

Finally, is there a function similar to Excel's "IFERROR" to get rid of the "infinity" values"?

Thank you!

[lbendlin]

The Power Query code is to be taken as is, and put into the advanced editor of a blank query, replacing whatever boilerplate code is there.

The first two lines of that are basically the data and schema of your sample table.

Power BI has a concept of "calculated columns" and "measures" - those are two very different things with different computations. You chose columns, that's what the formulas serve up.

The DIVIDE() code allows for alternative results to avoid dividing by zero, and DAX also has IF(ISBLANK()) patterns to help you decide what to do in case nothing is returned.

[Anonymous]

Thank you. So the PowerQuery has created a table called "LogN" with only one column called "LogN", which stores only one text value, which is the PowerQuery code itself.

Not sure if this was intended.

[lbendlin]

No. Not like this.

Create a blank query. Right click it. Select Advanced Editor. Replace the existing code with the one from my post.

[Anonymous]

Just a quick follow-up. I notice that the data is hard-coded from the json. How can I point NewsObs to the actual column in the data table that goes beyond these dates in my example?

[lbendlin]

Change the "Source = " line to point to your actual data.

[Anonymous]

Thank you SO much! That worked.