orsf {aorsf}  R Documentation 
Fit an oblique random survival forest
orsf(
data,
formula,
control = orsf_control_fast(),
weights = NULL,
n_tree = 500,
n_split = 5,
n_retry = 3,
mtry = NULL,
leaf_min_events = 1,
leaf_min_obs = 5,
split_min_events = 5,
split_min_obs = 10,
split_min_stat = 3.841459,
oobag_pred_type = "surv",
oobag_pred_horizon = NULL,
oobag_eval_every = n_tree,
oobag_fun = NULL,
importance = "anova",
group_factors = TRUE,
tree_seeds = NULL,
attach_data = TRUE,
no_fit = FALSE,
na_action = "fail",
verbose_progress = FALSE,
...
)
orsf_train(object)
data 
a data.frame, tibble, or data.table that contains the relevant variables. 
formula 
(formula) The response on the left hand side should include a time variable, followed by a status variable, and may be written inside a call to Surv (see examples). The terms on the right are names of predictor variables. 
control 
(orsf_control) An object returned from one of the

weights 
(numeric vector) Optional. If given, this input should
have length equal to Use 
n_tree 
(integer) the number of trees to grow.
Default is 
n_split 
(integer) the number of cutpoints assessed when splitting
a node in decision trees. Default is 
n_retry 
(integer) when a node can be split, but the current
linear combination of inputs is unable to provide a valid split, 
mtry 
(integer) Number of predictors randomly included as candidates
for splitting a node. The default is the smallest integer greater than
the square root of the number of total predictors, i.e.,

leaf_min_events 
(integer) minimum number of events in a
leaf node. Default is 
leaf_min_obs 
(integer) minimum number of observations in a
leaf node. Default is 
split_min_events 
(integer) minimum number of events required
in a node to consider splitting it. Default is 
split_min_obs 
(integer) minimum number of observations required
in a node to consider splitting it. Default is 
split_min_stat 
(double) minimum test statistic required to split a node. Default is 3.841459 for the logrank test, which is roughly a pvalue of 0.05 
oobag_pred_type 
(character) The type of outofbag predictions to compute while fitting the ensemble. Valid options are
Mortality ('mort')is not implemented for out of bag predictions yet, but it will be in a future update. 
oobag_pred_horizon 
(numeric) A numeric value indicating what time
should be used for outofbag predictions. Default is the median
of the observed times, i.e., 
oobag_eval_every 
(integer) The outofbag performance of the
ensemble will be checked every 
oobag_fun 
(function) to be used for evaluating outofbag prediction accuracy every
For more details, see the outofbag vignette. 
importance 
(character) Indicate method for variable importance:
For details on these methods, see orsf_vi. 
group_factors 
(logical) Only relevant if variable importance is
being estimated. if 
tree_seeds 
(integer vector) Optional. if specified, random seeds
will be set using the values in 
attach_data 
(logical) if 
no_fit 
(logical) if 
na_action 
(character) what should happen when

verbose_progress 
(logical) if 
... 
Further arguments passed to or from other methods (not currently used). 
object 
an untrained 'aorsf' object, created by setting

This function is based on and similar to the ORSF
function
in the obliqueRSF
R package. The primary difference is that this
function runs much faster. The speed increase is attributable to better
management of memory (i.e., no unnecessary copies of inputs) and using
a Newton Raphson scoring algorithm to identify linear combinations of
inputs rather than performing penalized regression using routines in
glmnet
.The modified Newton Raphson scoring algorithm that this
function applies is an adaptation of the C++ routine developed by
Terry M. Therneau that fits Cox proportional hazards models
(see survival::coxph()
and more specifically survival::coxph.fit()
).
an accelerated oblique RSF object (aorsf
)
formula:
The response in formula
can be a survival
object as returned by the Surv function,
but can also just be the time and status variables. I.e.,
Surv(time, status) ~ .
works just like time + status ~ .
A .
symbol on the right hand side is shorthand for using all
variables in data
(omitting those on the left hand side of
formula
) as predictors.
The order of variables in the left hand side matters. i.e.,
writing status + time ~ .
will make orsf
assume your
status
variable is actually the time
variable.
The response variable can be a survival object stored in data
.
For example, y ~ . is a valid formula if data$y
inherits
from the Surv
class.
Although you can fit an oblique random survival forest with 1 predictor variable, your formula should have at least 2 predictors. The reason for this recommendation is that a linear combination of predictors is trivial if there is only one predictor.
mtry:
The mtry
parameter may be temporarily reduced to ensure there
are at least 2 events per predictor variable. This occurs when using
orsf_control_cph because coefficients in the Newton Raphson scoring
algorithm may become unstable when the number of covariates is
greater than or equal to the number of events. This reduction does not
occur when using orsf_control_net.
oobag_fun:
If oobag_fun
is specified, it will be used in to compute negation
importance or permutation importance, but it will not have any role
for ANOVA importance.
Decision trees are developed by splitting a set of training data into two new subsets, with the goal of having more similarity within the new subsets than between them. This splitting process is repeated on the resulting subsets of data until a stopping criterion is met. When the new subsets of data are formed based on a single predictor, the decision tree is said to be axisbased because the splits of the data appear perpendicular to the axis of the predictor. When linear combinations of variables are used instead of a single variable, the tree is oblique because the splits of the data are neither parallel nor at a right angle to the axis
Figure : Decision trees for classification with axisbased splitting (left) and oblique splitting (right). Cases are orange squares; controls are purple circles. Both trees partition the predictor space defined by variables X1 and X2, but the oblique splits do a better job of separating the two classes.
Random forests are collections of decorrelated decision trees. Predictions from each tree are aggregated to make an ensemble prediction for the forest. For more details, see Breiman at el, 2001.
In random forests, each tree is grown with a bootstrapped version of the training set. Because bootstrap samples are selected with replacement, each bootstrapped training set contains about twothirds of instances in the original training set. The 'outofbag' data are instances that are not in the bootstrapped training set. Each tree in the random forest can make predictions for its outofbag data, and the outofbag predictions can be aggregated to make an ensemble outofbag prediction. Since the outofbag data are not used to grow the tree, the accuracy of the ensemble outofbag predictions approximate the generalization error of the random forest. Generalization error refers to the error of a random forest's predictions when it is applied to predict outcomes for data that were not used to train it, i.e., testing data.
Data passed to aorsf functions are not allowed to have missing values.
A user should impute missing values using an R package with that purpose,
such as recipes
or mlr3pipelines
.
First we load some relevant packages
set.seed(329730) suppressPackageStartupMessages({ library(aorsf) library(survival) library(tidymodels) library(tidyverse) library(randomForestSRC) library(ranger) library(riskRegression) library(obliqueRSF) })
The entrypoint into aorsf
is the standard call to orsf()
:
fit < orsf(pbc_orsf, Surv(time, status) ~ .  id)
printing fit
provides quick descriptive summaries:
fit
##  Oblique random survival forest ## ## Linear combinations: Accelerated ## N observations: 276 ## N events: 111 ## N trees: 500 ## N predictors total: 17 ## N predictors per node: 5 ## Average leaves per tree: 24 ## Min observations in leaf: 5 ## Min events in leaf: 1 ## OOB stat value: 0.84 ## OOB stat type: Harrell's Cstatistic ## Variable importance: anova ## ## 
For these examples we will make use of the orsf_control_
functions to
build and compare models based on their outofbag predictions. We will
also standardize the outofbag samples using the input argument
tree_seeds
The accelerated ORSF ensemble is the default because it has a nice balance of computational speed and prediction accuracy. It runs a single iteration of Newton Raphson scoring on the Cox partial likelihood function to find linear combinations of predictors.
fit_accel < orsf(pbc_orsf, control = orsf_control_fast(), formula = Surv(time, status) ~ .  id, tree_seeds = 1:500)
orsf_control_cph
runs Cox regression in each nonterminal node of each
survival tree, using the regression coefficients to create linear
combinations of predictors:
fit_cph < orsf(pbc_orsf, control = orsf_control_cph(), formula = Surv(time, status) ~ .  id, tree_seeds = 1:500)
orsf_control_net
runs penalized Cox regression in each nonterminal
node of each survival tree, using the regression coefficients to create
linear combinations of predictors. This can be really helpful if you
want to do feature selection within the node, but it is a lot slower
than the other options.
fit_net < orsf(pbc_orsf, # select 3 predictors out of 5 to be used in # each linear combination of predictors. control = orsf_control_net(df_target = 3), formula = Surv(time, status) ~ .  id, tree_seeds = 1:500)
Let’s make two customized functions to identify linear combinations of predictors.
The first uses random coefficients
f_rando < function(x_node, y_node, w_node){ matrix(runif(ncol(x_node)), ncol=1) }
The second derives coefficients from principal component analysis.
f_pca < function(x_node, y_node, w_node) { # estimate two principal components. pca < stats::prcomp(x_node, rank. = 2) # use the second principal component to split the node pca$rotation[, 2L, drop = FALSE] }
We can plug these functions into orsf_control_custom()
, and then pass
the result into orsf()
:
fit_rando < orsf(pbc_orsf, Surv(time, status) ~ .  id, control = orsf_control_custom(beta_fun = f_rando), tree_seeds = 1:500) fit_pca < orsf(pbc_orsf, Surv(time, status) ~ .  id, control = orsf_control_custom(beta_fun = f_pca), tree_seeds = 1:500)
So which fit seems to work best in this example? Let’s find out by evaluating the outofbag survival predictions.
risk_preds < list( accel = 1  fit_accel$pred_oobag, cph = 1  fit_cph$pred_oobag, net = 1  fit_net$pred_oobag, rando = 1  fit_rando$pred_oobag, pca = 1  fit_pca$pred_oobag ) sc < Score(object = risk_preds, formula = Surv(time, status) ~ 1, data = pbc_orsf, summary = 'IPA', times = fit_accel$pred_horizon)
The AUC values, from highest to lowest:
sc$AUC$score[order(AUC)]
## model times AUC se lower upper ## 1: net 1788 0.9107925 0.02116880 0.8693024 0.9522826 ## 2: accel 1788 0.9106308 0.02178112 0.8679406 0.9533210 ## 3: cph 1788 0.9072690 0.02120139 0.8657150 0.9488229 ## 4: pca 1788 0.8915619 0.02335399 0.8457889 0.9373349 ## 5: rando 1788 0.8900944 0.02228487 0.8464168 0.9337719
And the indices of prediction accuracy:
sc$Brier$score[order(IPA), .(model, times, IPA)]
## model times IPA ## 1: accel 1788 0.4891448 ## 2: cph 1788 0.4687734 ## 3: net 1788 0.4652211 ## 4: rando 1788 0.4011573 ## 5: pca 1788 0.3845911 ## 6: Null model 1788 0.0000000
From inspection,
the PCA approach has the highest discrimination, showing that you can do very well with just a two line custom function.
the accelerated ORSF has the highest index of prediction accuracy
the random coefficients generally don’t do that well.
This example uses tidymodels
functions but stops short of using an
official tidymodels
workflow. I am working on getting aorsf
pulled
into the censored
package and I will update this with real workflows
if that happens!
Start with a recipe to preprocess data
imputer < recipe(pbc_orsf, formula = time + status ~ .) %>% step_impute_mean(all_numeric_predictors()) %>% step_impute_mode(all_nominal_predictors())
Next create a 10fold cross validation object and preprocess the data:
# 10fold cross validation; make a container for the preprocessed data analyses < vfold_cv(data = pbc_orsf, v = 10) %>% mutate(recipe = map(splits, ~prep(imputer, training = training(.x))), train = map(recipe, juice), test = map2(splits, recipe, ~bake(.y, new_data = testing(.x)))) analyses
## # 10fold crossvalidation ## # A tibble: 10 x 5 ## splits id recipe train test ## <list> <chr> <list> <list> <list> ## 1 <split [248/28]> Fold01 <recipe> <tibble [248 x 20]> <tibble [28 x 20]> ## 2 <split [248/28]> Fold02 <recipe> <tibble [248 x 20]> <tibble [28 x 20]> ## 3 <split [248/28]> Fold03 <recipe> <tibble [248 x 20]> <tibble [28 x 20]> ## 4 <split [248/28]> Fold04 <recipe> <tibble [248 x 20]> <tibble [28 x 20]> ## 5 <split [248/28]> Fold05 <recipe> <tibble [248 x 20]> <tibble [28 x 20]> ## 6 <split [248/28]> Fold06 <recipe> <tibble [248 x 20]> <tibble [28 x 20]> ## 7 <split [249/27]> Fold07 <recipe> <tibble [249 x 20]> <tibble [27 x 20]> ## 8 <split [249/27]> Fold08 <recipe> <tibble [249 x 20]> <tibble [27 x 20]> ## 9 <split [249/27]> Fold09 <recipe> <tibble [249 x 20]> <tibble [27 x 20]> ## 10 <split [249/27]> Fold10 <recipe> <tibble [249 x 20]> <tibble [27 x 20]>
Define functions for a ‘workflow’ with randomForestSRC
, ranger
, and
aorsf
.
rfsrc_wf < function(train, test, pred_horizon){ # rfsrc does not like tibbles, so cast input data into data.frames train < as.data.frame(train) test < as.data.frame(test) rfsrc(formula = Surv(time, status) ~ ., data = train) %>% predictRisk(newdata = test, times = pred_horizon) %>% as.numeric() } ranger_wf < function(train, test, pred_horizon){ ranger(Surv(time, status) ~ ., data = train) %>% predictRisk(newdata = test, times = pred_horizon) %>% as.numeric() } aorsf_wf < function(train, test, pred_horizon){ train %>% orsf(Surv(time, status) ~ .,) %>% predict(new_data = test, pred_horizon = pred_horizon) %>% as.numeric() }
Run the ‘workflows’ on each fold:
# 5 year risk prediction ph < 365.25 * 5 results < analyses %>% transmute(test, pred_aorsf = map2(train, test, aorsf_wf, pred_horizon = ph), pred_rfsrc = map2(train, test, rfsrc_wf, pred_horizon = ph), pred_ranger = map2(train, test, ranger_wf, pred_horizon = ph))
Next unnest each column to get back a tibble
with all of the testing
data and predictions.
results < results %>% unnest(everything()) glimpse(results)
## Rows: 276 ## Columns: 23 ## $ id <int> 2, 16, 27, 66, 79, 97, 107, 116, 136, 137, 158, 189, 193, ~ ## $ trt <fct> d_penicill_main, placebo, placebo, d_penicill_main, d_peni~ ## $ age <dbl> 56.44627, 40.44353, 54.43943, 46.45311, 46.51608, 71.89322~ ## $ sex <fct> f, f, f, m, f, m, f, f, f, f, f, f, f, f, f, f, f, f, f, f~ ## $ ascites <fct> 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0~ ## $ hepato <fct> 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1~ ## $ spiders <fct> 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1~ ## $ edema <fct> 0, 0, 0.5, 0, 0, 0.5, 0, 0.5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0~ ## $ bili <dbl> 1.1, 0.7, 21.6, 1.4, 0.8, 2.0, 0.6, 3.0, 0.8, 1.1, 3.4, 1.~ ## $ chol <int> 302, 204, 175, 427, 315, 420, 212, 458, 263, 399, 450, 360~ ## $ albumin <dbl> 4.14, 3.66, 3.31, 3.70, 4.24, 3.26, 4.03, 3.63, 3.35, 3.60~ ## $ copper <int> 54, 28, 221, 105, 13, 62, 10, 74, 27, 79, 32, 52, 267, 76,~ ## $ alk.phos <dbl> 7394.8, 685.0, 3697.4, 1909.0, 1637.0, 3196.0, 648.0, 1588~ ## $ ast <dbl> 113.52, 72.85, 101.91, 182.90, 170.50, 77.50, 71.30, 106.9~ ## $ trig <int> 88, 58, 168, 171, 70, 91, 77, 382, 69, 152, 118, 164, 157,~ ## $ platelet <int> 221, 198, 80, 123, 426, 344, 316, 438, 206, 344, 313, 256,~ ## $ protime <dbl> 10.6, 10.8, 12.0, 11.0, 10.9, 11.4, 17.1, 9.9, 9.8, 10.1, ~ ## $ stage <ord> 3, 3, 4, 3, 3, 3, 1, 3, 2, 2, 2, 3, 4, 4, 2, 2, 3, 3, 4, 4~ ## $ time <int> 4500, 3672, 77, 4191, 3707, 611, 3388, 3336, 3098, 2990, 2~ ## $ status <dbl> 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0~ ## $ pred_aorsf <dbl> 0.21650571, 0.01569191, 0.93095617, 0.36737089, 0.12868206~ ## $ pred_rfsrc <dbl> 0.15202784, 0.01104486, 0.81913559, 0.20173550, 0.13806608~ ## $ pred_ranger <dbl> 0.11418963, 0.02130315, 0.77073269, 0.22130305, 0.18419972~
And finish by aggregating the predictions and computing performance in the testing data. Note that I am computing one statistic for all predictions instead of computing one statistic for each fold. This approach is fine when you have smaller testing sets and/or small event counts.
Score( object = list(aorsf = results$pred_aorsf, rfsrc = results$pred_rfsrc, ranger = results$pred_ranger), formula = Surv(time, status) ~ 1, data = results, summary = 'IPA', times = ph )
## ## Metric AUC: ## ## Results by model: ## ## model times AUC lower upper ## 1: aorsf 1826 90.1 85.7 94.6 ## 2: rfsrc 1826 89.4 85.0 93.7 ## 3: ranger 1826 90.1 85.9 94.3 ## ## Results of model comparisons: ## ## times model reference delta.AUC lower upper p ## 1: 1826 rfsrc aorsf 0.7 2.3 0.8 0.4 ## 2: 1826 ranger aorsf 0.0 1.7 1.6 1.0 ## 3: 1826 ranger rfsrc 0.7 0.4 1.8 0.2 ## ## NOTE: Values are multiplied by 100 and given in %. ## NOTE: The higher AUC the better. ## ## Metric Brier: ## ## Results by model: ## ## model times Brier lower upper IPA ## 1: Null model 1826.25 20.5 18.1 22.9 0.0 ## 2: aorsf 1826.25 11.1 8.8 13.4 45.8 ## 3: rfsrc 1826.25 12.0 9.8 14.1 41.6 ## 4: ranger 1826.25 11.8 9.7 13.9 42.5 ## ## Results of model comparisons: ## ## times model reference delta.Brier lower upper p ## 1: 1826.25 aorsf Null model 9.4 12.1 6.6 2.423961e11 ## 2: 1826.25 rfsrc Null model 8.5 10.8 6.2 2.104905e13 ## 3: 1826.25 ranger Null model 8.7 11.0 6.4 1.802417e13 ## 4: 1826.25 rfsrc aorsf 0.9 0.0 1.7 5.277607e02 ## 5: 1826.25 ranger aorsf 0.7 0.1 1.5 1.008730e01 ## 6: 1826.25 ranger rfsrc 0.2 0.7 0.3 4.550782e01 ## ## NOTE: Values are multiplied by 100 and given in %. ## NOTE: The lower Brier the better, the higher IPA the better.
From inspection,
aorsf
obtained slightly higher discrimination (AUC)
aorsf
obtained higher index of prediction accuracy (IPA)
Way to go, aorsf
Warning: this code may or may not run depending on your current
version of mlr3proba
. First we load some additional mlr3
libraries.
suppressPackageStartupMessages({ library(mlr3verse) library(mlr3proba) library(mlr3extralearners) library(mlr3viz) library(mlr3benchmark) })
Next we’ll define some tasks for our learners to engage with.
# Mayo Clinic Primary Biliary Cholangitis Data task_pbc < TaskSurv$new( id = 'pbc', backend = select(pbc_orsf, id) %>% mutate(stage = as.numeric(stage)), time = "time", event = "status" ) # Veteran's Administration Lung Cancer Trial data(veteran, package = "randomForestSRC") task_veteran < TaskSurv$new( id = 'veteran', backend = veteran, time = "time", event = "status" ) # NKI 70 gene signature data_nki < OpenML::getOMLDataSet(data.id = 1228) task_nki < TaskSurv$new( id = 'nki', backend = data_nki$data, time = "time", event = "event" ) # Gene ExpressionBased Survival Prediction in Lung Adenocarcinoma data_lung < OpenML::getOMLDataSet(data.id = 1245) task_lung < TaskSurv$new( id = 'nki', backend = data_lung$data %>% mutate(OS_event = as.numeric(OS_event) 1), time = "OS_years", event = "OS_event" ) # Chemotherapy for Stage B/C colon cancer # (there are two rows per person, one for death # and the other for recurrence, hence the two tasks) task_colon_death < TaskSurv$new( id = 'colon_death', backend = survival::colon %>% filter(etype == 2) %>% drop_na() %>% # drop id, redundant variables select(id, study, node4, etype), mutate(OS_event = as.numeric(OS_event) 1), time = "time", event = "status" ) task_colon_recur < TaskSurv$new( id = 'colon_death', backend = survival::colon %>% filter(etype == 1) %>% drop_na() %>% # drop id, redundant variables select(id, study, node4, etype), mutate(OS_event = as.numeric(OS_event) 1), time = "time", event = "status" ) # putting them all together tasks < list(task_pbc, task_veteran, task_nki, task_lung, task_colon_death, task_colon_recur, # add a few more premade ones tsk("actg"), tsk('gbcs'), tsk('grace'), tsk("unemployment"), tsk("whas"))
Now we can make a benchmark designed to compare our three favorite learners:
# Learners with default parameters learners < lrns(c("surv.ranger", "surv.rfsrc", "surv.aorsf")) # Brier (Graf) score, cindex and training time as measures measures < msrs(c("surv.graf", "surv.cindex", "time_train")) # Benchmark with 5fold CV design < benchmark_grid( tasks = tasks, learners = learners, resamplings = rsmps("cv", folds = 5) ) benchmark_result < benchmark(design) bm_scores < benchmark_result$score(measures, predict_sets = "test")
Let’s look at the overall results:
bm_scores %>% select(task_id, learner_id, surv.graf, surv.cindex, time_train) %>% group_by(learner_id) %>% filter(!is.infinite(surv.graf)) %>% summarize( across( .cols = c(surv.graf, surv.cindex, time_train), .fns = mean, na.rm = TRUE ) )
## # A tibble: 3 x 4 ## learner_id surv.graf surv.cindex time_train ## <chr> <dbl> <dbl> <dbl> ## 1 surv.aorsf 0.151 0.729 0.345 ## 2 surv.ranger 0.167 0.706 2.54 ## 3 surv.rfsrc 0.156 0.715 0.783
From inspection,
aorsf
appears to have a higher expected value for ‘surv.cindex’
(higher is better)
aorsf
appears to have a lower expected value for ‘surv.graf’ (lower
is better)
aorsf
has the lowest training time.
the lower training time for aorsf
is likely due to the fact that there
are many unique event times in the benchmark tasks. ranger
and rfsrc
create grids of time points based on each unique event time in each leaf
of each decision tree, whereas aorsf
also uses a grid but restricts it
to the unique event times among observations in the current leaf.
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Jaeger BC, Long DL, Long DM, Sims M, Szychowski JM, Min YI, Mcclure LA, Howard G, Simon N. Oblique random survival forests. Annals of applied statistics 2019 Sep; 13(3):184783. DOI: 10.1214/19AOAS1261
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