R cumulative sum by condition with reset

by

Here’s one way with ave:

ave(df$a, cumsum(c(F, diff(df$a) < 0)), FUN=seq_along) - 1
 [1] 0 1 2 3 0 1 2 3 4 5 6 0 1 0

We can get a running count grouped by diff(df$a) < 0. Which are the positions in the vector that are less than their predecessors. We add c(F, ..) to account for the first position. The cumulative sum of that vector creates an index for grouping. The function ave can carry out a function on that index, we use seq_along for a running count. But since it starts at 1, we subtract by one ave(...) - 1 to start from zero.

A similar approach using dplyr:

library(dplyr)
df %>% 
  group_by(cumsum(c(FALSE, diff(a) < 0))) %>% 
  mutate(row_number() - 1)

More Related Contents:

  1. Replace missing values (NA) with most recent non-NA by group
  2. Getting the top values by group
  3. Group by multiple columns in dplyr, using string vector input
  4. R spreading multiple columns with tidyr [duplicate]
  5. Select groups which have at least one of a certain value
  6. Display / print all rows of a tibble (tbl_df)
  7. Proper idiom for adding zero count rows in tidyr/dplyr
  8. Why is enquo + !! preferable to substitute + eval
  9. Add NAs to make all list elements equal length
  10. Assign intermediate output to temp variable as part of dplyr pipeline
  11. pass function arguments to both dplyr and ggplot
  12. Removing NA observations with dplyr::filter()
  13. Mutate multiple columns in a dataframe
  14. dplyr issues when using group_by(multiple variables)
  15. dplyr – using mutate() like rowmeans()
  16. dplyr piping data – difference between `.` and `.x`
  17. Filling missing dates in a grouped time series – a tidyverse-way?
  18. mutate_each / summarise_each in dplyr: how do I select certain columns and give new names to mutated columns?
  19. Spread with duplicate identifiers (using tidyverse and %>%) [duplicate]
  20. Cartesian product with dplyr
  21. Difference between rbind() and bind_rows() in R
  22. Canonical tidyverse method to update some values of a vector from a look-up table
  23. Categorize continuous variable with dplyr [duplicate]
  24. How to combine ggplot and dplyr into a function?
  25. R: Using a string as an argument to mutate verb in dplyr
  26. dplyr: put count occurrences into new variable [duplicate]
  27. How to replace empty string with NA in R dataframe?
  28. Add row in each group using dplyr and add_row()
  29. How to replace certain values in a specific rows and columns with NA in R?
  30. Add margin row totals in dplyr chain

Leave a Comment