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Anonymous's avatar
Anonymous
Not applicable
6 years ago
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Custom Query/Function to convert UTC to EST

I am pulling a  number of datetime columns from several sources, which are mostly in UTC. I'm using ToLocal to display these in EST, which is my local time, and is how my end users need to see the data.

 

However this does not work in the report after publishing to the PowerBI service, which seems to use UTC as its local time.

If my data source reads 18:00 UTC, ToLocal has no effect on the data -- it is still shown as 18:00 in the PowerBI Service.

 

A simple solution would just be to subtract X hours from my UTC times in PowerQuery. The data would "look" like EST in PowerBI Desktop, and will "look" like EST in the PowerBI service (even though PowerBI thinks it is a UTC time).

 

However this does not account for daylight savings at all, which isn't trivial, because DST starts and ends on a different day each year.

 

So I'd like an M function (or some other creative approach) that can...

 

  • Read in a DateTime that is in UTC
  • Check if that DateTime falls into Daylight Savings
    • If yes, subtract 5 hours
    • If no, subtract 4 hours
  • Be easily applied to multiple columns

 

Any ideas?

  • To get the local timezone, use the following function, which I created in a blank query.

     

     

    = DateTimeZone.SwitchZone(DateTimeZone.LocalNow(),-7)

     

     

    Change the -7 to your normal non-DST offset.

     

    I also called that query varToday

     

    Now create another query like this:

     

     

    let
        Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("LczBDcAwCATBXvy2BIcT2anFov82ErL+7WkEe7dhCgvXbL1JdtPZf1GthVz0Ea/1IING1jfCAdHnpB6EkElnvg==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [dtDSTStart = _t, dtDSTEnd = _t]),
        #"Changed Type" = Table.TransformColumnTypes(Source,{{"dtDSTStart", type date}, {"dtDSTEnd", type date}}),
        #"Filtered Rows" = Table.SelectRows(#"Changed Type", each (DateTime.Date(varToday) >= [dtDSTStart] and DateTime.Date(varToday) <= [dtDSTEnd])),
        #"Counted Rows" = Table.RowCount(#"Filtered Rows")
    in
        #"Counted Rows"

     

     

    That will return a 1 or 0. 1 if we are in DST, 0 if not. I called this query varDST Note it references varToday above.

     

    Now all other functions should be using the same logic as the DateTimeZone.SwitchZone([UTC],-7) but you add varDST, which will either add 1 or 0.

     

    1) In Power Query, select New Source, then Blank Query
    2) On the Home ribbon, select "Advanced Editor" button
    3) Remove everything you see, then paste the M code I've given you in that box.
    4) Press Done

     

    EDIT: This will not property work in the wee hours of the morning on DST switch dates. It assumes the entire day is or is not DST. YOu'd need to greatly expand the table to handle the 2am-3am switch.

10 Replies

  • edhans's avatar
    edhans
    Community Champion

    To get the local timezone, use the following function, which I created in a blank query.

     

     

    = DateTimeZone.SwitchZone(DateTimeZone.LocalNow(),-7)

     

     

    Change the -7 to your normal non-DST offset.

     

    I also called that query varToday

     

    Now create another query like this:

     

     

    let
        Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("LczBDcAwCATBXvy2BIcT2anFov82ErL+7WkEe7dhCgvXbL1JdtPZf1GthVz0Ea/1IING1jfCAdHnpB6EkElnvg==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [dtDSTStart = _t, dtDSTEnd = _t]),
        #"Changed Type" = Table.TransformColumnTypes(Source,{{"dtDSTStart", type date}, {"dtDSTEnd", type date}}),
        #"Filtered Rows" = Table.SelectRows(#"Changed Type", each (DateTime.Date(varToday) >= [dtDSTStart] and DateTime.Date(varToday) <= [dtDSTEnd])),
        #"Counted Rows" = Table.RowCount(#"Filtered Rows")
    in
        #"Counted Rows"

     

     

    That will return a 1 or 0. 1 if we are in DST, 0 if not. I called this query varDST Note it references varToday above.

     

    Now all other functions should be using the same logic as the DateTimeZone.SwitchZone([UTC],-7) but you add varDST, which will either add 1 or 0.

     

    1) In Power Query, select New Source, then Blank Query
    2) On the Home ribbon, select "Advanced Editor" button
    3) Remove everything you see, then paste the M code I've given you in that box.
    4) Press Done

     

    EDIT: This will not property work in the wee hours of the morning on DST switch dates. It assumes the entire day is or is not DST. YOu'd need to greatly expand the table to handle the 2am-3am switch.

    • Anonymous's avatar
      Anonymous
      Not applicable

      edhans This is helpful, but I'm not sure it's 100% what I need.

      This query relies on the current date to determine if we're in DST or not, no? The solution needs to check the date which is being converted.

      Imagine I have three years worth of data all in UTC, and need to convert them all to EST. Thoughts?

      The solution will have to be some custom function that takes the date as an input, rather than relying on varToday. I'm just not well versed enough in M to write it!

      • edhans's avatar
        edhans
        Community Champion

        Just change the function to pull your field, vs the current time.

         

        = DateTimeZone.SwitchZone(DateTimeZone.LocalNow(),-7)
        
        becomes
        
        = DateTimeZone.SwitchZone([YourUTCDateTimeZoneField],-7)

         

         

        In otherwords you would not use varToday. Just add a custom column that might ahve this full formula

        = DateTimeZone.SwitchZone([YourUTCDateTimeZoneField],-7 + varDST)

         

        Make sense? If not, send back some data via links below and a screen shot from Excel of expected output.

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