# Understanding rolling calculations in R

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In R, we often need to get values or perform calculations from information not on the same row. We need to either retrieve specific values or we need to produce some sort of aggregation. This post explores some of the options and explains the weird (to me at least!) behaviours around rolling calculations and alignments.
We can retrieve earlier values by using the lag() function from dplyr[1]. This by default looks one value earlier in the sequence.
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