R data.table binary value for last row in group by condition

Question

I have data like this:

library(data.table)
id <- c(\"1232\",\"1232\",\"1232\",\"4211\",\"4211\",\"4211\")
conversion <- c(0,0,0,1,1,1)
DT <- data.ta         


        

Answer 1

Timings for reference:

library(data.table)
#data.table 1.12.3 IN DEVELOPMENT built 2019-05-12 17:04:48 UTC; root using 4 threads (see ?getDTthreads).  Latest news: r-datatable.com
set.seed(0L)
nid <- 3e6L
DT <- data.table(id=rep(1L:nid, each=3L))[,
    conversion := sample(c(0L,1L), 1L, replace=TRUE), by=.(id)]
DT0 <- copy(DT)
DT1 <- copy(DT)
DT2 <- copy(DT)
DT3 <- copy(DT)

mtd0 <- function() {
    DT0[DT0[, .I[.N], by=id]$V1, lastconv := conversion]
    DT0[is.na(lastconv), lastconv := 0L]
}

mtd1 <- function() {
    DT1[DT1[, .I[.N], by=id]$V1, lastconv := conversion]
    setnafill(DT1, cols = "lastconv", fill = 0L)
}

mtd2 <- function() {
    DT2[, v := 0]
    DT2[.(DT2[conversion == 1, unique(id)]), on=.(id), mult="last", v := 1]

    #or also
    #DT2[, v := 0L][
    #    DT2[,.(cv=last(conversion)), id], on=.(id), mult="last", v := cv]
}

mtd3 <- function() {
    DT3[ , lastconv := as.integer(.I == .I[.N] & conversion == 1), by = id]
}

library(microbenchmark)
microbenchmark(mtd0(), mtd1(), mtd2(), mtd3(), times=1L)

timings:

Unit: milliseconds
   expr       min        lq      mean    median        uq       max neval cld
 mtd0() 1363.1783 1416.1867 1468.9256 1469.1952 1521.7992 1574.4033     3  b 
 mtd1() 1349.5333 1365.4653 1378.9350 1381.3974 1393.6358 1405.8743     3  b 
 mtd2()  511.5615  515.4728  552.9133  519.3841  573.5892  627.7944     3 a  
 mtd3() 3966.8867 4009.1128 4048.9607 4051.3389 4089.9977 4128.6564     3   c

Answer 2

For each id, check if row number is the last row number in the group, and if 'conversion' is 1. Convert logical result to integer.

DT[ , lastconv := as.integer(.I == .I[.N] & conversion == 1), by = id]

Answer 3

Modifying the OP's code to join on the last row of each group:

DT[, v := 0]
DT[.(DT[conversion == 1, unique(id)]), on=.(id), mult="last", v := 1]

     id conversion v
1: 1232          0 0
2: 1232          0 0
3: 1232          0 0
4: 4211          1 0
5: 4211          1 0
6: 4211          1 1

This is only different in that it selects which ids to edit based on the desired condition.

Answer 4

Filter for the last row per group and set lastconv equal to conversion.

DT[DT[, .I[.N], by=id]$V1, lastconv := conversion]

Then replace NAs with 0

DT[is.na(lastconv), lastconv := 0L]

Result

DT
#     id conversion lastconv
#1: 1232          0        0
#2: 1232          0        0
#3: 1232          0        0
#4: 4211          1        0
#5: 4211          1        0
#6: 4211          1        1

---

If data.table v1.12.3 is installed we could also use the new function setnafill to replace NAs in the second step

DT[DT[, .I[.N], by=id]$V1, lastconv := conversion]
setnafill(DT, cols = "lastconv", fill = 0L)

Answer 5

Have you tried something like the following?

library(tidyverse)

final_conversion_dat <- DT %>% 
  group_by(id) %>% 
  mutate(date = as.Date(date),
         final_conversion = ifelse(date == max(date, na.rm = T) & conversion == 1, 1, 0))