2021: Week 15 - Solution

Solution by Tom Prowse and you can download the workflow here. 

This week we looked at a property management challenge, where we wanted to calculate the amount of rental revenue that our company is making from it's portfolio. The challenge was created by Tom Smith (@tSmithyyy) so let's take a look at how to solve it. 

Step 1 - Contract Length

First we want to calculate the length of each contract in months. To do this we want to input the Rental Contracts data then use a DateDiff calculation to find the length of the contract in months: 

Contract Length 

DATEDIFF('month', [Contract Start], [Contract End])

Then we can calculate how many months are left until the contract expires:

Months Until Expiry 

DATEDIFF('month', MAKEDATE(2022,04,13), [Contract End])

Then finally we can find the month of the contract start and end month by using the following calculations:

Contract Start Month

DATE(DATETRUNC('month',[Contract Start]))

Contract End Month
DATE(DATETRUNC('month',[Contract End]))

At this stage our table should look like this: 

Step 2 - Combine Prices

Next we want to combine both the rental contracts and the office space prices tables, by joining them using and inner join on the City and Office Size fields: 

From here we can remove any duplicated fields as a result of the join (City-1 & Office Size-1).

Step 3 - Create Rows

We now want to create a new row of data for each month that the property will be rented. To do this we can use the 'New Rows' step within Tableau Prep to help us pad out the missing rows based on the start and end dates.

The New Rows step should have the following setup: 

As a result our contract lengths should now be split out so there is a row for each month that the contract is live: 

Then after creating the new rows, we need to ensure that the final month isn't included, therefore we need to filter to exclude these values using: [Contract End Month]!=[Month Divider]

After this we can remove the Contract Start and End Month fields from our view.

Step 4 - Cumulative Cost

Next we want to calculate the cumulative cost of each monthly rental space contract. We can calculate this by using the following calculation: 

Cumulative Monthly Cost 

{ PARTITION [Company] : 

{ ORDERBY [Month Divider] ASC : WINDOW_SUM([Rent per Month])}

}

At this stage we have our first output that looks like this:

Step 5 - Total Paid Rent

For the second output we want to calculate the total amount of rent that has been paid across time. 

First we need to identify whether the value is from a completed year or needs to be included in a year to date calculation. We can identify these by using the following calculation: 

EoY or Current 

IF 

MAKEDATE(2022,04,13)

> 

[Month Divider]

THEN [Rent per Month] END

Then we can convert our Month Divider field into just the Year: 

Year

YEAR([Month Divider])

At this stage we are ready to aggregate our table to calculate the totals that are required. Using the aggregation tool we can group by Year and the Sum EoY and Current:

As a result we have our 2nd output that looks like this: 

You can download the full outputs here. 

After you finish the challenge make sure to fill in the participation tracker, then share your solution on Twitter using #PreppinData and tagging @tSmithyyy, @Datajedininja, @JennyMartinDS14 & @TomProwse1

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