did you mean to say flag or lag in the exercise? exercise 11says:
Write code that adds a variable to the data frame data that lags V4
# with 1 value. Important: the first value of each ID should be NA.
my question is:
is "lag" a typo?
Answers and follow-up questions Answer or follow-up question 1
It's definitely lag. I've updated the exercise with more explanations.
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