Exercise

First differences

Now that we know how to take lags, generating first-differences is pretty straightforward. The first-difference of a time series just involves taking each value and subtracting the value observed at the previous time period.

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Instructions 1/3

XP

1
- Add a column called sales_lag1 that holds the one-period lag in "sales"
2
- Add the one-period difference in sales, sales_diff1, using the precomputed lag column.
3
- Add the two-period difference in sales, sales_diff2, without referencing the precomputed lag column.