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Excerpt

This example covers how to use the NEXT function to create windows of data from the current row and subsequent (next) rows in the dataset. You can then apply rolling computations across these windows of data.

Functions:

D generate list excerpts
pages NEXT Function,ROLLINGAVERAGE Function,NUMFORMAT Function

Source:

The following dataset contains order information for the preceding 12 months. You want to compare the current month's average against the preceding quarter.

DateAmount
12/31/15118
11/30/156
10/31/15443
9/30/15785
8/31/1577
7/31/15606
6/30/15421
5/31/15763
4/30/15305
3/31/15824
2/28/15135
1/31/15523

Transformation:

Using the `ROLLINGAVERAGE` function, you can generate a column containing the rolling average of the current month and the two previous months:

D trans
RawWrangle true step window value: ROLLINGAVERAGE(Amount, 3, 0) order: -Date Formulas ROLLINGAVERAGE(Amount, 3, 0) Order by -Date Window

Note the sign of the second parameter and the `order` parameter. The sort is in the reverse order of the `Date` parameter, which preserves the current sort order. As a result, the second parameter, which identifies the number of rows to use in the calculation, must be positive to capture the previous months.

Technically, this computation does not capture the prior quarter, since it includes the current quarter as part of the computation. You can use the following column to capture the rolling average of the preceding month, which then becomes the true rolling average for the prior quarter. The `window` column refers to the name of the column generated from the previous step:

D trans
RawWrangle true step window value: NEXT(window, 1) order: -Date Formulas NEXT(window, 1) Order by -Date Window

Note that the order parameter must be preserved. This new column, `window1`, contains your prior quarter rolling average:

D trans
RawWrangle true 'Amount_PriorQtr' step rename col:window1 to:'Amount_PriorQtr' Option Manual rename Column window1 New column name Rename columns

You can reformat this numeric value:

D trans
RawWrangle true step set col:Amount_PriorQtr value:NUMFORMAT(Amount_PriorQtr, '###.00') Columns Amount_PriorQtr Formula NUMFORMAT(Amount_PriorQtr, '###.00') Edit column with formula

You can use the following transformation to calculate the net change. This formula computes the change as a percentage of the prior quarter and then formats it as a two-digit percentage.

D trans
RawWrangle true 'NetChangePct_PriorQtr' step derive type:single value:NUMFORMAT(((Amount - Amount_PriorQtr) / Amount_PriorQtr) * 100, '##.##') as:'NetChangePct_PriorQtr' Formula type Single row formula Formula NUMFORMAT(((Amount - Amount_PriorQtr) / Amount_PriorQtr) * 100, '##.##') New column name New formula

Results:

Info

NOTE: You might notice that there are computed values for `Amount_PriorQtr` for February and March. These values do not factor in a full three months because the data is not present. The January value does not exist since there is no data preceding it.

DateAmountAmount_PriorQtrNetChangePct_PriorQtr
12/31/15118411.33-71.31
11/30/156435.00-98.62
10/31/15443489.33-9.47
9/30/15785368.00113.32
8/31/1577596.67-87.1
7/31/15606496.3322.1
6/30/15421630.67-33.25
5/31/15763421.3381.09
4/30/15305494.00-38.26
3/31/15824329.00150.46
2/28/15135523.00-.74.19
1/31/15523

D s also
label example_next_function