Power Query: Rental Wrangles
28 July 2021
Welcome to our Power Query blog. This week, I look at how to expand data to create a useful table.
I have some data on tent rentals:
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It’s a fairly basic Table, which just records the date when rentals for each type of tent change.
I also have a Table of one-day events, where tent rental is required:
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I want to know the rental for each event, but currently there is only a clear link for the first event, as it occurs on 1 January 2021 and there is a rental rate entry for this. There are a couple of ways I can approach this. This week, I am going to expand the tent rental table so that there is an entry for every date.
I start by extracting the tent rental data to Power Query, using ‘From Table/Range’ on the ‘Get & Transform Data’ section of the Data tab.
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I start by ordering my data by Tent Type, using the dropdown next to the column heading.
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I need to get the Tent Type into the headings so that I can cross reference Tent Type with all Dates in the appropriate period. I can do this by pivoting the Tent Type column. This option is available from the Transform tab:
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I now have column headings for each Tent Type.
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In order to create a row for each Date, I am going to create a new Blank Query from the ‘New Source’ dropdown in the ‘New Query’ section of the Home tab.
I start my new query by using functionality that will create a list. The M code I am going to use is in the form:
={fromdate..todate}
However, I can not currently use dates as the beginning and ending points; I have to use numbers. Power Query will then generate every number in the interval. Thus, I convert my dates to numbers.
= {Number.From(#date(2021,1,1))..Number.From(#date(2021,6,1))}
Here, I am creating a date by providing the year, month and day number, and then using Number.From() to convert the date to a number. This will give me a number for every day from 1 January 2021 to 1 June 2021.
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I can then convert the list to a table using the option on the ‘List Tools’ tab. I also change the datatype to DateTime (so that it matches the Date column on my original query) and rename it Date.
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My Calendar query is ready to use.
Back in my original query (now called Rental Calendar), I am going to merge with the Calendar query. I can do this from the Home tab.
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I use a ‘Right Outer’ join because I want to include every Date from Calendar.
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I can now expand the Calendar column to just give me the Date.
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I remove the original Date column. I need a rental value for every date, so I can fill down on “Large”, “Medium” and “Small”.
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Finally, I need to get the tent types back into a Tent Type column. I can do this by selecting Date and choosing to ‘Unpivot other columns’ from the ‘Unpivot Columns’ dropdown on the Transform tab.
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I now have a value for each date, telling me what the rental is for each type of tent. I can rename the Attribute and Value columns to Tent Type and Rental Rate.
Next, I extract the data for the events:
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I merge with the query Rental Calendar. This time, I use a ‘Left Outer’ join, as I only want rows for each Event Date and Tent Type.
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This gives me a new column containing the data from Rental Calendar.
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I expand Rental Calendar to get the Rental Rate.
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Next time, I’ll look at a different way to get to this result by creating a function.
Come back next time for more ways to use Power Query!