Help with Date_request in Date.IsInPreviousNMonths

[Anders_G]

Hi,

I'm trying to manage my data imports with date filters. I want to import X months in the past from the previous year. I've read you can change the date_request in the Date.IsInPreviousNMonths([date_request], 2) function.

I've tried creating a custom date query from a blank query and giving it today's date one year in the past. I've named the query Datefilter.

My custom function then looks like this.

= Table.SelectRows(Dataset_(LY)_View, each Date.IsInPreviousNMonths(Datefilter, 2))

However, it doesn't return any data. What am I doing wrong?

[Rickmaurinus]

Hi there,

The Date.IsInPreviousNMonths function tests whether a date value is within the specified number of months, compared from your current system time. 

For your filter to work,  you should change around the 'DateFilter' variable, to a date column that's actually within your query. For instance, if you have a [Sales Date] column you could use: 

Table.SelectRows(Dataset_(LY)_View, each Date.IsInPreviousNMonths([Sales Date], 2))

More details here: https://powerquery.how/date-isinpreviousnmonths

However, if you want to filter on dates starting from last year, you would need something like: 

Table.SelectRows( 
  Dataset_(LY)_View, 
  each [Sales Data] < Date.AddYears( Date.From( DateTime.LocalNow() ), -1 )
    and [Sales Data] >= Date.AddMonths( Date.From( DateTime.LocalNow() ), -14 )
)

In that way you filter your data down to the relevant dates. 

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[v-yueyunzh-msft]

Hi , @Anders_G 

The "Date.IsInPreviousNMonths" function is automatically compared with the current time of the system, and the comparison date cannot be customized.

For more information, you can refer to:
Date.IsInPreviousNMonths - PowerQuery M | Microsoft Learn

If you want to  import X months in the past from the previous year .  I think you need to calculate the days between two days and then compare the days to filter your table.

Best Regards,

Aniya Zhang

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[Anders_G]

Thank you for the clarification.

If you want to  import X months in the past from the previous year .  I think you need to calculate the days between two days and then compare the days to filter your table.

I would be very grateful if you could explain the process in more detail. I have no real knowledge of M or SQL. I mostly copy and paste what I can find on this forum. 

[v-yueyunzh-msft · Accepted solution]

Hi , @Anders_G 

Accoding to your description, you want to filter the previous N months od the last year. Right?

I mean this , you can put this in "Advanced Editor" in Power Query Editor:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("Tc3BDQAhCETRXjib4ODqQi3G/ttYJJrl+vIzMydJFWEwqBBolQsu3UnkGsLGtpbQGLoNTwrrCZEsHsYPnc3h1SOw2HfS5lPrAw==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, value = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}, {"value", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", (x)=>if Duration.Days(Date.AddDays(Date.From(Date.From(DateTime.LocalNow())),-365)-x[Date]) >=0 and  Duration.Days(Date.AddDays(Date.From(Date.From(DateTime.LocalNow())),-365)-x[Date]) <=60  then 1 else -1          )
in
    #"Added Custom"

The table is like this:

Then we can filter the [Custom]=1 then we will meet your need .

Best Regards,

Aniya Zhang

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