Last updated: 2023-06-16

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Rmd 7de25c8 Charlotte Boys 2023-06-16 Publish main parts of framework

Introduction

Next, we prepare the data so it is ready for joint modelling. Since we are interested in the chronic eGFR trajectory, we filter out the episodes flagged as AKI and in-patient events.

Load necessary libraries:

library(tidyverse)
── Attaching core tidyverse packages ──────────────────────── tidyverse 2.0.0 ──
✔ dplyr     1.1.2     ✔ readr     2.1.4
✔ forcats   1.0.0     ✔ stringr   1.5.0
✔ ggplot2   3.4.2     ✔ tibble    3.2.1
✔ lubridate 1.9.2     ✔ tidyr     1.3.0
✔ purrr     1.0.1     
── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──
✖ dplyr::filter() masks stats::filter()
✖ dplyr::lag()    masks stats::lag()
ℹ Use the conflicted package (<http://conflicted.r-lib.org/>) to force all conflicts to become errors

Load data:

patient_metadata <- read.csv("data/simulated_metadata.csv")
flagged_episodes <- read.csv("output/flagged_episodes.csv")
longitudinal_data <- read.csv("output/longitudinal_data.csv")

Filter out measurements during AKI episodes

First, let’s remind ourselves of how the flagged episodes data looked:

knitr::kable(head(flagged_episodes))
start end patient_id n_obs flag
1 5 2 4 AKI
2759 2759 2 1 AKI
3893 3893 2 1 AKI
6192 6192 2 1 AKI
6234 6234 2 1 AKI
0 13 3 5 in-patient

There were three types of flags:

unique(flagged_episodes$flag)
[1] "AKI"                "in-patient"         "AKI and in-patient"

We define a function to filter out the flagged episodes:

filter_flagged_episodes <- function(longitudinal_data,
                                    flagged_episodes,
                                    flags = c("AKI and in-patient", "AKI")){
  to_remove <- flagged_episodes %>%
  dplyr::filter(flag %in% flags)
  
  patients_without_flags <- longitudinal_data %>%
  dplyr::filter(!(patient_id %in% to_remove$patient_id)) %>%
  dplyr::distinct()
  
  patients_with_flags <- longitudinal_data %>%
  dplyr::filter(patient_id %in% to_remove$patient_id)
  
  check_observations <- dplyr::left_join(patients_with_flags,
                          to_remove,
                          by = "patient_id",
                          multiple = "all",
                          relationship = "many-to-many") %>%
  dplyr::mutate(flagged = ifelse(days_from_biopsy >= start & days_from_biopsy <= end, TRUE, FALSE))

  patients_with_flags_keep <- check_observations %>%
    dplyr::group_by(patient_id, days_from_biopsy) %>%
    dplyr::filter(!any(flagged == TRUE)) %>%
    dplyr::select(-c(start, end, n_obs, flag, flagged)) %>%
    dplyr::distinct()
  
  patients_with_flags_remove <- check_observations %>%
    dplyr::group_by(patient_id, days_from_biopsy) %>%
    dplyr::filter(any(flagged == TRUE)) %>%
    dplyr::select(-c(start, end, n_obs, flag, flagged)) %>%
    dplyr::distinct()
  
  stopifnot("Sum of rows to keep and rows to remove does not equal original number of rows" = nrow(patients_with_flags_keep) + nrow(patients_with_flags_remove) == nrow(patients_with_flags))
  
  measurements_filtered <- rbind(patients_without_flags, patients_with_flags_keep)
  return(measurements_filtered)
}

We filter the eGFR measurements, removing those taken during episodes of care flagged as meeting both the AKI and in-patient criteria:

eGFR_filtered <- filter_flagged_episodes(longitudinal_data,
                                         flagged_episodes,
                                         flags = c("AKI and in-patient")) %>%
  dplyr::filter(type == "eGFR")

Prepare eGFR data for joint modelling

In our simulated longitudinal data, we only have one clinical endpoint event of interest: dialysis. We gather information about which patients reached the clinical endpoint, at which event time:

endpoints <- c("Dialysis")

event_time <- longitudinal_data %>% 
  dplyr::filter(type %in% endpoints) %>%
  dplyr::transmute(patient_id, event_time = days_from_biopsy)

reached_endpoint <- event_time$patient_id

Add information about endpoints and final measurement time to the patient metadata:

final_measurement <- longitudinal_data %>%
  dplyr::group_by(patient_id) %>%
  dplyr::slice_max(days_from_biopsy, n = 1, with_ties = F) %>% 
  dplyr::transmute(patient_id, last_measurement = days_from_biopsy)

patient_metadata <- patient_metadata %>% 
  dplyr::full_join(final_measurement, 
                   by = "patient_id" ,
                   multiple = "all") %>%
  dplyr::full_join(event_time, by = "patient_id", multiple = "all") %>%
  dplyr::distinct() %>%
  dplyr::group_by(patient_id) %>%
  dplyr::slice_head(n = 1) # Keep only one entry per patient_id

We add the patient metadata to the filtered longitudinal eGFR data, and also rescale measurements from days to years. We add the columns start, stop and endpoint as they are needed for the joint modelling:

eGFR_plus_metadata <- dplyr::full_join(eGFR_filtered, 
                                 patient_metadata, 
                                 by = c('patient_id')) %>%
  dplyr::mutate(last_measurement_y = last_measurement/365.25,
                event_time_y = event_time/365.25) %>%
  dplyr::distinct() %>%
  tidyr::drop_na(years_from_biopsy) %>%
  dplyr::group_by(patient_id) %>%
  dplyr::arrange(years_from_biopsy) %>%
  dplyr::mutate(start = years_from_biopsy) %>%
  dplyr::mutate(stop = dplyr::lead(start,
                                   order_by = years_from_biopsy,
                                   default = unique(last_measurement_y))) %>%
  dplyr::mutate(event = ifelse(is.na(event_time_y),
                               0,
                               ifelse(abs(stop-event_time_y) < 1e-10,
                                      1,
                                      0))) %>% 
  dplyr::mutate(endpoint = ifelse(patient_id %in% reached_endpoint,
                                  1, 
                                  0))

We have just a few more changes to make to be able to run the joint modelling.

Surv() requires the start time to be different from the stop time of the interval. However, when an observation is the last available measurement for that patient, the start and the stop time are equal. As a work around, we omit the final observations from the model:

to_omit <- eGFR_plus_metadata %>% dplyr::filter(stop <= start)
eGFR_plus_metadata <- setdiff(eGFR_plus_metadata, to_omit)

JM does not accept start times of zero. We have to set them to a small positive number. Also, create a minimal dataframe of only the variables we will use in the modelling process, check that patient_id is numeric, and order the data according to patient_id and start time:

eGFR_minimal <- eGFR_plus_metadata %>% 
  dplyr::select(patient_id, last_measurement_y, endpoint, measurement, disease, age_at_biopsy, sex, start, stop, event) %>%
  dplyr::mutate(start = ifelse(start < 1/365.25, 1e-5, start))

stopifnot("`patient_id` is not numeric" = all(is.numeric(eGFR_minimal$patient_id)))

# Order the longitudinal data according to the patient_id, and order the time points within each subject with respect to time
eGFR_minimal <- eGFR_minimal[order(eGFR_minimal$patient_id, eGFR_minimal$start),]
knitr::kable(head(eGFR_minimal))
patient_id last_measurement_y endpoint measurement disease age_at_biopsy sex start stop event
1 9.514031 0 83.08316 B 29 M 0.0054757 0.0191650 0
1 9.514031 0 82.96855 B 29 M 0.0191650 0.0273785 0
1 9.514031 0 88.61724 B 29 M 0.0273785 0.0301164 0
1 9.514031 0 83.85820 B 29 M 0.0301164 0.7091034 0
1 9.514031 0 94.30087 B 29 M 0.7091034 0.9637235 0
1 9.514031 0 94.39833 B 29 M 0.9637235 1.4510609 0

Save data

write.csv(eGFR_minimal, "output/eGFR_minimal.csv", row.names = FALSE)

sessionInfo()
R version 4.3.0 (2023-04-21)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Monterey 12.4

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRblas.0.dylib 
LAPACK: /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.11.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

time zone: Europe/Rome
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] lubridate_1.9.2 forcats_1.0.0   stringr_1.5.0   dplyr_1.1.2    
 [5] purrr_1.0.1     readr_2.1.4     tidyr_1.3.0     tibble_3.2.1   
 [9] ggplot2_3.4.2   tidyverse_2.0.0 workflowr_1.7.0

loaded via a namespace (and not attached):
 [1] sass_0.4.6       utf8_1.2.3       generics_0.1.3   stringi_1.7.12  
 [5] hms_1.1.3        digest_0.6.31    magrittr_2.0.3   timechange_0.2.0
 [9] evaluate_0.21    grid_4.3.0       fastmap_1.1.1    rprojroot_2.0.3 
[13] jsonlite_1.8.5   processx_3.8.1   whisker_0.4.1    ps_1.7.5        
[17] promises_1.2.0.1 httr_1.4.6       fansi_1.0.4      scales_1.2.1    
[21] jquerylib_0.1.4  cli_3.6.1        rlang_1.1.1      munsell_0.5.0   
[25] withr_2.5.0      cachem_1.0.8     yaml_2.3.7       tools_4.3.0     
[29] tzdb_0.4.0       colorspace_2.1-0 httpuv_1.6.11    vctrs_0.6.2     
[33] R6_2.5.1         lifecycle_1.0.3  git2r_0.32.0     fs_1.6.2        
[37] pkgconfig_2.0.3  callr_3.7.3      pillar_1.9.0     bslib_0.4.2     
[41] later_1.3.1      gtable_0.3.3     glue_1.6.2       Rcpp_1.0.10     
[45] xfun_0.39        tidyselect_1.2.0 rstudioapi_0.14  knitr_1.43      
[49] htmltools_0.5.5  rmarkdown_2.22   compiler_4.3.0   getPass_0.2-2