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Cumsum() function

As explained in Statistics Slam Dunk

The cumsum() function returns the cumulative sums of the elements in a numeric vector.

cumsum() returns a vector of cumulative sums from another numeric vector. For 1, 2, and 3, it returns 1, 3, and 6. section 6.4.1

Build cumulative NBA totals

After counting first-quarter outcome categories and sorting them by frequency, add cumulative counts with mutate(cum_n = cumsum(n)). The resulting values are 783, 1333, 1698, and 1990; cumsum(pct_total) similarly produces cumulative percentages ending at 100.00. section 6.4.1

How Statistics Slam Dunk covers it

How deep it goes
Defines cumulative summation, demonstrates a three-value vector, and applies it inside mutate(); it does not explain implementation internals.
Examples
Uses the vector 1, 2, 3 and first-quarter NBA outcome counts to produce cumulative counts and percentages.
What it assumes
Assumes numeric vectors and basic dplyr pipelines while defining cumulative sums from a simple vector.
What you can do after
Apply it via R and dplyr to create running totals and cumulative percentages in a data frame.
How it connects
Connects cumulative summation with dplyr, mutate(), count(), arrange(), percentages, and data visualization.
Cover of Statistics Slam Dunk
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This explainer was generated by Manning's knowledge graph from the text of Statistics Slam Dunk. The section links point to the parts of the book it draws on.