R - MLR - Classifier Calibration - Benchmark Results - mlr

Question

I've run a benchmark experiment with nested cross validation (tuning + performance measurement) for a classification problem and would like to create calibration charts.
If I pass a benchmark result object to generateCalibrationData, what does plotCalibration do? Is it averaging? If so how?
Does it make sense to have an aggregate = FALSE option to understand variability across folds as per generateThreshVsPerfData for ROC curves?
In response to #Zach's request for a reproducible example, I (the OP) edit my original post as follows:
Edit: Reproducible Example
# Practice Data
library("mlr")
library("ROCR")
library(mlbench)
data(BreastCancer)
dim(BreastCancer)
levels(BreastCancer$Class)
head(BreastCancer)
BreastCancer <- BreastCancer[, -c(1, 6, 7)]
BreastCancer$Cl.thickness <- as.factor(unclass(BreastCancer$Cl.thickness))
BreastCancer$Cell.size <- as.factor(unclass(BreastCancer$Cell.size))
BreastCancer$Cell.shape <- as.factor(unclass(BreastCancer$Cell.shape))
BreastCancer$Marg.adhesion <- as.factor(unclass(BreastCancer$Marg.adhesion))
head(BreastCancer)
# Define Nested Cross-Validation Strategy
cv.inner <- makeResampleDesc("CV", iters = 2, stratify = TRUE)
cv.outer <- makeResampleDesc("CV", iters = 6, stratify = TRUE)
# Define Performance Measures
perf.measures <- list(auc, mmce)
# Create Task
bc.task <- makeClassifTask(id = "bc",
data = BreastCancer,
target = "Class",
positive = "malignant")
# Create Tuned KSVM Learner
ksvm <- makeLearner("classif.ksvm",
predict.type = "prob")
ksvm.ps <- makeParamSet(makeDiscreteParam("C", values = 2^(-2:2)),
makeDiscreteParam("sigma", values = 2^(-2:2)))
ksvm.ctrl <- makeTuneControlGrid()
ksvm.lrn = makeTuneWrapper(ksvm,
resampling = cv.inner,
measures = perf.measures,
par.set = ksvm.ps,
control = ksvm.ctrl,
show.info = FALSE)
# Create Tuned Random Forest Learner
rf <- makeLearner("classif.randomForest",
predict.type = "prob",
fix.factors.prediction = TRUE)
rf.ps <- makeParamSet(makeDiscreteParam("mtry", values = c(2, 3, 5)))
rf.ctrl <- makeTuneControlGrid()
rf.lrn = makeTuneWrapper(rf,
resampling = cv.inner,
measures = perf.measures,
par.set = rf.ps,
control = rf.ctrl,
show.info = FALSE)
# Run Cross-Validation Experiments
bc.lrns = list(ksvm.lrn, rf.lrn)
bc.bmr <- benchmark(learners = bc.lrns,
tasks = bc.task,
resampling = cv.outer,
measures = perf.measures,
show.info = FALSE)
# Calibration Charts
bc.cal <- generateCalibrationData(bc.bmr)
plotCalibration(bc.cal)
Produces the following:
Aggregared Calibration Plot
Attempting to un-aggregate leads to:
> bc.cal <- generateCalibrationData(bc.bmr, aggregate = FALSE)
Error in generateCalibrationData(bc.bmr, aggregate = FALSE) :
unused argument (aggregate = FALSE)
>
> sessionInfo()
R version 3.2.3 (2015-12-10)
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] mlbench_2.1-1 ROCR_1.0-7 gplots_3.0.1 mlr_2.9
[5] stringi_1.1.1 ParamHelpers_1.10 ggplot2_2.1.0 BBmisc_1.10
loaded via a namespace (and not attached):
[1] digest_0.6.9 htmltools_0.3.5 R6_2.2.0 splines_3.2.3
[5] scales_0.4.0 assertthat_0.1 grid_3.2.3 stringr_1.0.0
[9] bitops_1.0-6 checkmate_1.8.2 gdata_2.17.0 survival_2.38-3
[13] munsell_0.4.3 tibble_1.2 randomForest_4.6-12 httpuv_1.3.3
[17] parallelMap_1.3 mime_0.5 DBI_0.5-1 labeling_0.3
[21] chron_2.3-47 shiny_1.0.0 KernSmooth_2.23-15 plyr_1.8.4
[25] data.table_1.9.6 magrittr_1.5 reshape2_1.4.1 kernlab_0.9-25
[29] ggvis_0.4.3 caTools_1.17.1 gtable_0.2.0 colorspace_1.2-6
[33] tools_3.2.3 parallel_3.2.3 dplyr_0.5.0 xtable_1.8-2
[37] gtools_3.5.0 backports_1.0.4 Rcpp_0.12.4

Answer 1

no plotCalibration doesn't do any averaging, though it can plot a smooth.
if you call generateCalibrationData on a benchmark result object it will treat each iteration of your resampled predictions as exchangeable and compute the calibration across all resampled predictions for that bin.
yes it probably would make sense to have an option to generate an unaggregated calibration data object and be able to plot it. you are welcome to open an issue on GitHub to that effect, but this is going to be low on my priority list TBH.