How to join two dataframes containing time varying variables in R - r

Question

This seems like a simple enough thing but I can't figure it out nor find an answer online - apologies if it something obvious. I have two seperate dataframes containing the same patients with the same unique identifier. Both datasets have time varying variables - one continuous and one categorical and the time to each reading is different in the sets but have a common start point at time 1. I have tried to modify the tmerge function from survival package but without luck as I don't have a dichotomous outcome variable nor a single data set with one row per patient.
Reprex for creating the datasets below (df1 and df2) and an example of my desired combined output table for a single patient (ID 3), output gets very long if done for all 4 patients
Thanks for any possible help
df1 <- structure(list(tstart = c(1, 1, 1, 1426, 1, 560, 567), tstop = c(2049,
3426, 1426, 1707, 560, 567, 4207), category = structure(c(1L,
1L, 1L, 2L, 1L, 4L, 2L), .Label = c("none", "high", "low", "moderate"
), class = "factor"), id = c(1L, 2L, 3L, 3L, 4L, 4L, 4L)), row.names = c(NA,
-7L), class = c("tbl_df", "tbl", "data.frame"))
df2 <- structure(list(tstart = c(1, 365, 730, 1, 365, 730, 1096, 2557,
1, 365, 730, 1096, 1826, 2557, 3652, 1), tstop = c(365, 730,
1096, 365, 730, 1096, 2557, 2582, 365, 730, 1096, 1826, 2557,
3652, 4864, 365), egfr = c(66, 62, 58, 54, 50, 43, 49, 51, 106,
103, 80, 92, 97, 90, 81, 51), id = c(1L, 1L, 1L, 2L,
2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L,
3L, 3L, 3L, 4L)), row.names = c(NA, -16L), class = c("tbl_df",
"tbl", "data.frame"))
df_example_patient_3 <- structure(list(id = c(3L, 3L, 3L,
3L, 3L, 3L,3L, 3L, 3L), tstart = c(1, 365, 730, 1096, 1426, 1707, 1826, 2557, 3652), tstop = c(365, 730,
1096, 1426, 1707, 1826, 2557, 3652, 4864), egfr = c(106, 103, 80, 92, 92, 92, 97, 90, 81), category = c("none", "none", "none", "none", "high", "high", "high", "high", "high")), row.names = c(NA, -9L), class = c("tbl_df",
"tbl", "data.frame"))
# DF1
tstart tstop category id
<dbl> <dbl> <fct> <int>
1 1 2049 none 1
2 1 3426 none 2
3 1 1426 none 3
4 1426 1707 high 3
5 1 560 none 4
6 560 567 moderate 4
7 567 4207 high 4
# DF2
tstart tstop egfr id
<dbl> <dbl> <dbl> <int>
1 1 365 66 1
2 365 730 62 1
3 730 1096 58 1
4 1 365 54 2
5 365 730 50 2
6 730 1096 43 2
7 1096 2557 49 2
8 2557 2582 51 2
9 1 365 106 3
10 365 730 103 3
11 730 1096 80 3
12 1096 1826 92 3
13 1826 2557 97 3
14 2557 3652 90 3
15 3652 4864 81 3
16 1 365 51 4
# Combined set
id tstart tstop egfr category
<int> <dbl> <dbl> <dbl> <chr>
1 3 1 365 106 none
2 3 365 730 103 none
3 3 730 1096 80 none
4 3 1096 1426 92 none
5 3 1426 1707 92 high
6 3 1707 1826 92 high
7 3 1826 2557 97 high
8 3 2557 3652 90 high
9 3 3652 4864 81 high

Answer 1

I had to do it this way to really work out the details.
First, i construct a full df1 with all the timestamps, including those of df2.
then i proceed with multiple merges. This is not elegant, but it works:
library(data.table)
library(zoo)
# Proper data.tables
setDT(df1, key = c("id", "tstart"))
setDT(df2, key = c("id", "tstart"))
timestamps_by_id <- unique(rbind(
df1[, .(id, tstart)],
df1[, .(id, tstop)],
df2[, .(id, tstart)],
df2[, .(id, tstop)],
use.names = F
))
setorder(timestamps_by_id, id, tstart)
# Merge to construct full df1
df1_full <- df1[timestamps_by_id]
df1_full[, category := na.locf(category), by = id]
df1_full[, tstop := shift(tstart, -1), by = id]
setkey(df1_full, id, tstart)
# Merge with df2
result <- na.omit(df2[df1_full, roll = T])
result[, tstop := i.tstop]
print(result[id == 3, .(id, tstart, tstop, egfr, category)])
Or a more data.tabley solution using the more arcane foverlaps:
library(data.table)
# Proper data.tables
setDT(df1, key = c("id", "tstart", "tstop"))
setDT(df2, key = c("id", "tstart", "tstop"))
# We add an infinite upper range
proper_df1 <- rbind(
df1,
df1[, .SD[which.max(tstop)], by = .(id)][, .(id, tstart = tstop, tstop = Inf, category), ]
)
setkey(proper_df1, id, tstart, tstop)
overlaps <- foverlaps(df2, proper_df1, type = "any") # Overlap join
overlaps[
tstart %between% .(i.tstart, i.tstop) & tstart != 1,
i.tstart := tstart
]
overlaps[tstop %between% .(i.tstart, i.tstop), i.tstop := tstop]
print(overlaps[
id == 3,
.(id, "tstart" = i.tstart, "tstop" = i.tstop, category, egfr)
])

Answer 2

This messy dplyr solution seems to work for this particular dataset but don't know would it work for all datasets, the direction of the fill may need to be altered depending on particular dataset
library(tidyverse)
library(magrittr)
df1 %>%
bind_rows(df2) %>%
group_by(id) %>%
arrange(id, tstop) %>%
mutate(
tstart = case_when(
tstart < lag(tstop) ~ lag(tstop), TRUE ~ tstart)) %>%
fill(egfr, category, .direction = "updown") %>%
ungroup() %>%
filter(id == 3)
tstart tstop category id egfr
<dbl> <dbl> <fct> <int> <dbl>
1 1 365 none 3 106
2 365 730 none 3 103
3 730 1096 none 3 80
4 1096 1426 none 3 92
5 1426 1707 high 3 92
6 1707 1826 high 3 92
7 1826 2557 high 3 97
8 2557 3652 high 3 90
9 3652 4864 high 3 81