How can i subtract current values from previous week values?

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gbrown
gbrown Member

Hello,

I am trying to subtract current week values with previous week values and have the ability for this to update each week. How would I do this in Magic ETL? A lag function?

So 5-19 week would subtract from 5-12 week and then next week I would like to see 5-26 week subtract from 5-19.

Thanks,

Garrett

Best Answers

  • david_cunningham
    edited May 22 Answer ✓
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    Assuming your data will always be grouped by week, you could use a lag function. You would use a Rank & Window tile to achieve this in ETL. One thing to keep in mind, is that lag will always go to the last value, so if you are missing data for a week, it would go back 2 weeks. If you want to avoid this, you will need to fill in your missing weeks by joining up a date dimension table.

    Here is an example of how you could set it up.

    Which yields the following

    David Cunningham

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  • david_cunningham
    Answer ✓
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    @gbrown it looks like you have this set up to lag 300 rows. Is that what you want?

    You can always test the output by running a preview in ETL, and then checking the output to see if it matches what your desired output is.

    David Cunningham

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  • GrantSmith
    GrantSmith Coach
    Answer ✓
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    I'd recommend restructuring your data with a custom date offset so you can easily calculate the prior week. I've done a write up on it here:

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Answers

  • david_cunningham
    edited May 22 Answer ✓
    Options

    Assuming your data will always be grouped by week, you could use a lag function. You would use a Rank & Window tile to achieve this in ETL. One thing to keep in mind, is that lag will always go to the last value, so if you are missing data for a week, it would go back 2 weeks. If you want to avoid this, you will need to fill in your missing weeks by joining up a date dimension table.

    Here is an example of how you could set it up.

    Which yields the following

    David Cunningham

    ** Was this post helpful? Click Agree 😀, Like 👍️, or Awesome ❤️ below **
    ** Did this solve your problem? Accept it as a solution! ✔️**

  • gbrown
    gbrown Member
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    Thanks. Is this how I would set up the lag function? @david_cunningham

  • david_cunningham
    Answer ✓
    Options

    @gbrown it looks like you have this set up to lag 300 rows. Is that what you want?

    You can always test the output by running a preview in ETL, and then checking the output to see if it matches what your desired output is.

    David Cunningham

    ** Was this post helpful? Click Agree 😀, Like 👍️, or Awesome ❤️ below **
    ** Did this solve your problem? Accept it as a solution! ✔️**

  • GrantSmith
    GrantSmith Coach
    Answer ✓
    Options

    I'd recommend restructuring your data with a custom date offset so you can easily calculate the prior week. I've done a write up on it here:

    **Was this post helpful? Click Agree or Like below**
    **Did this solve your problem? Accept it as a solution!**