R: Group by time index and collapse with 'summarise()'

index_by {tsibble}

R Documentation

Group by time index and collapse with `summarise()`

Description

index_by() is the counterpart of group_by() in temporal context, but it only groups the time index. The following operation is applied to each partition of the index, similar to group_by() but dealing with index only. index_by() + summarise() will update the grouping index variable to be the new index. Use ungroup() to remove the index grouping vars.

Usage

index_by(.data, ...)

Arguments

.data

A tbl_ts.

...

If empty, grouping the current index. Or a single expression contains an existing variable or a name-value pair. The index functions that can be used, but not limited:

lubridate::year: yearly aggregation
yearquarter: quarterly aggregation
yearmonth: monthly aggregation
yearweek: weekly aggregation
as.Date or lubridate::as_date: daily aggregation
lubridate::ceiling_date, lubridate::floor_date, or lubridate::round_date: fine-resolution aggregation
other index functions from other packages

Details

A index_by()-ed tsibble is indicated by @ in the "Groups" when displaying on the screen.

Examples

pedestrian %>% index_by()
# Monthly counts across sensors
library(dplyr, warn.conflicts = FALSE)
monthly_ped <- pedestrian %>% 
  group_by_key() %>% 
  index_by(Year_Month = yearmonth(Date_Time)) %>%
  summarise(
    Max_Count = max(Count),
    Min_Count = min(Count)
  )
monthly_ped
index(monthly_ped)

# Using existing variable
pedestrian %>% 
  group_by_key() %>% 
  index_by(Date) %>%
  summarise(
    Max_Count = max(Count),
    Min_Count = min(Count)
  )

# Attempt to aggregate to 4-hour interval, with the effects of DST
pedestrian %>% 
  group_by_key() %>% 
  index_by(Date_Time4 = lubridate::floor_date(Date_Time, "4 hour")) %>%
  summarise(Total_Count = sum(Count))

# Annual trips by Region and State
tourism %>% 
  index_by(Year = lubridate::year(Quarter)) %>% 
  group_by(Region, State) %>% 
  summarise(Total = sum(Trips))