February 7, 2011

When Totals Don’t Work

Qlikview (QV) provides for three types of totals in straight tables and pivot tables:
  • None
  • The expression calculated at the total level
  • Aggregate function (sum, average, minimum etc) of the table rows

These options cover most cases, but sometimes you have a table where none of these options is appropriate, or provides the correct result. As an example, consider a table of absolute variances, such as budget amount vs selling amount, on a table dimensioned by product class. The expression for the variance and % variance would be:

[AbsoluteVariance] = Fabs(Sum(BudgetAmount) - Sum(SellingAmount))

[%AbsoluteVariance] = Fabs(Sum(BudgetAmount) - Sum(SellingAmount)) / Sum(BudgetAmount)


These expressions yield different results for a different degree of dimensioning, so the sum of the absolute variances per ProductClass is not the same as the absolute variance at the total level. Therefore, the AbsoluteVariance column needs to be totalled using the Sum of rows option. For the %AbsoluteVariance, however, the expression at the total level does not work for the same reason, and the summing of the rows is arithmetically meaningless. In this example, a total is required for both of these columns.

So, how do we construct an expression that will produce the correct %AbsoluteVariance for each row and for the total?

We have the expression for the rows:

[%AbsoluteVariance] = Fabs(Sum(BudgetAmount) - Sum(SellingAmount)) / Sum(BudgetAmount)

For the total, we need an expression like:

[%AbsoluteVariance] = Sum(Rows of AbsoluteVariance) / Sum(BudgetAmount)

Assuming that ProductClass was the only dimension on the table, the Sum(Rows of AbsoluteVariance) can be calculated as follows:

Sum(Aggr(Fabs(Sum(BudgetAmount) – Sum(SellingAmount)), ProductClass))

So, how do we differentiate between the two expressions?

This is where the QV Dimensionality() function comes in. In our case, Dimensionality() will return zero when calculated on the total row, and greater than zero elsewhere. Check the Qlikview Reference Manual for more information on the function.

Our final expression becomes:

If(Dimensionality() = 0,
// total row expression
Sum(Aggr(Fabs(Sum(BudgetAmount) – Sum(SellingAmount)), ProductClass)) / Sum(BudgetAmount),
// other row expression
Fabs(Sum(BudgetAmount) - Sum(SellingAmount)) / Sum(BudgetAmount))

QED

Unzip the download here and play around with a sample QVW model and the Excel source file.

2 comments:

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