replyr (version 0.3.01)

gapply: grouped ordered apply

Description

Partitions from by values in grouping column, applies a generic transform to each group and then binds the groups back together. Only advised for a moderate number of groups and better if grouping column is an index. This is powerfull enough to implement "The Split-Apply-Combine Strategy for Data Analysis" https://www.jstatsoft.org/article/view/v040i01

Usage

gapply(df, gcolumn, f, ..., ocolumn = NULL, decreasing = FALSE,
  partitionMethod = "split", bindrows = TRUE, maxgroups = 100,
  eagerCompute = FALSE, restoreGroup = FALSE,
  tempNameGenerator = makeTempNameGenerator("replyr_gapply"))

Arguments

df

remote dplyr data item

gcolumn

grouping column

f

transform function or pipleline

...

force later values to be bound by name

ocolumn

ordering column (optional)

decreasing

logical, if TRUE sort in decreasing order by ocolumn

partitionMethod

method to partition the data, one of 'group_by' (depends on f being dplyr compatible), 'split' (only works over local data frames), or 'extract'

bindrows

logical, if TRUE bind the rows back into a data item, else return split list

maxgroups

maximum number of groups to work over (intentionally not enforced if partitionMethod=='group_by')

eagerCompute

logical, if TRUE call compute on split results

restoreGroup

logical, if TRUE restore group column after apply when partitionMethod %in% c('extract', 'split')

tempNameGenerator

temp name generator produced by replyr::makeTempNameGenerator, used to record dplyr::compute() effects.

Value

transformed frame

Details

Note this is a fairly expensive operator, so it only makes sense to use in situations where f itself is fairly complicated and/or expensive.

Examples

library('dplyr')
d <- data.frame(group=c(1,1,2,2,2),
                order=c(.1,.2,.3,.4,.5),
                values=c(10,20,2,4,8))

# User supplied window functions.  They depend on known column names and
# the data back-end matching function names (as cumsum).
cumulative_sum <- . %>% mutate(cv=cumsum(values))
rank_in_group <- . %>% mutate(constcol=1) %>%
          mutate(rank=cumsum(constcol)) %>% select(-constcol)

for(partitionMethod in c('group_by','split','extract')) {
  print(partitionMethod)
  print('cumulative sum example')
  print(d %>% gapply('group',cumulative_sum,ocolumn='order',
                     partitionMethod=partitionMethod))
  print('ranking example')
  print(d %>% gapply('group',rank_in_group,ocolumn='order',
                     partitionMethod=partitionMethod))
  print('ranking example (decreasing)')
  print(d %>% gapply('group',rank_in_group,ocolumn='order',decreasing=TRUE,
                     partitionMethod=partitionMethod))
}