Продвинутые агрегации

Работа с данными с помощью data.table в R

Matt Dowle, Arun Srinivasan

Instructors, DataCamp

Повторение

# Same example as seen before
## LHS := RHS Form
batrips[, c("is_dur_gt_1hour", "week_day") := 
            .(duration > 3600, wday(start_date)]

# Same as above, but in `:=`() functional form
batrips[, `:=`(is_dur_gt_1hour = duration > 3600,
               week_day = wday(start_date))]

# Update by reference with by
batrips[, n_zip_code := .N, by = zip_code]

Добавление нескольких столбцов по ссылке с группировкой

# Functional form
batrips[, `:=`(end_dur_first = duration[1], 
               end_dur_last  = duration[.N]),
        by = end_station]

# LHS := RHS form
batrips[, c("end_dur_first", 
            "end_dur_last") := list(duration[1], duration[.N]), 
        by = end_station]

batrips[1:5]

   trip_id duration ...        end_station ... end_dur_first end_dur_last 
    139545      435 ...    Townsend at 7th ...           435          660
    139546      432 ...    Townsend at 7th ...           435          660
    139547     1523 ...    Beale at Market ...          1523          229
    139549     1620 ... Powell Street BART ...          1620          540
    139550     1617 ... Powell Street BART ...          1620          540

Разбивка значений по категориям

Для каждой уникальной комбинации start_station и end_station — если медианная продолжительность:

менее 600 — «short»
от 600 до 1800 — «medium»
в остальных случаях — «long»

Многострочные выражения в j

batrips[, trip_category := {
             med_dur = median(duration, na.rm = TRUE)
             if (med_dur < 600) "short"
             else if (med_dur >= 600 & med_dur <= 1800) "medium"
             else "long"
           },
        by = .(start_station, end_station)]
batrips[1:3]

trip_id duration ... zip_code trip_category
 139545      435 ...    94612         short
 139546      432 ...    94107         short
 139547     1523 ...    94112         short

Альтернативный подход

bin_median_duration <- function(dur) {
  med_dur <- median(dur, na.rm = TRUE)
  if (med_dur < 600) "short"
  else if (med_dur >= 600 & med_dur <= 1800) "medium"
  else "long"
}

batrips[, trip_category := bin_median_duration(duration), 
           by = .(start_station, end_station)]

Всё вместе — i, j и by

batrips[duration > 500, min_dur_gt_500 := min(duration), 
           by = .(start_station, end_station)]
batrips[1:3]

trip_id duration ... zip_code min_dur_gt_500
 139545      435 ...    94612             NA
 139546      432 ...    94107             NA
 139547     1523 ...    94112            502

Давайте потренируемся!

Работа с данными с помощью data.table в R