고급 집계

R의 data.table로 데이터 조작하기

Matt Dowle, Arun Srinivasan

Instructors, DataCamp

복습

# 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]

그룹별로 여러 열을 참조로 추가하기

# 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

값 구간화

start_station과 end_station의 고유 조합별로, 소요 시간의 중앙값이:

600 미만이면 "short"
600 이상 1800 이하이면 "medium"
그 외에는 "long"

j에서 여러 줄 표현식 사용하기

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

대안적 방법

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)]

i, j, by 함께 사용하기

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

연습해 봅시다!

R의 data.table로 데이터 조작하기