Error in custom measure parsing external function while using parallelization - parallel-processing

Question

I defined a custom measure that allows to transform the prediction$data with an external function before evaluating standard measures such as rmse. If I try to tune params without parallelization everything goes smooth but if I start a parallelized session it seems not to find the external function anymore, although it's declared in the global environment.
library(compiler)
library(mlr)
library(parallelMap)
library(parallel)
# define function
inverse_fun = function(x){x^2}
inverse_fun = Vectorize(inverse_fun)
inverse_fun = cmpfun(inverse_fun, options=list(suppressUndefined=T))
assign('inverse_fun', inverse_fun, envir = .GlobalEnv)
tuning_criterion = 'rmse'
# define a new measure that applies inverse_fun to prediction and evaluates rmse
original_measure = eval(parse(text=tuning_criterion))
transf_measure_fun = function(task, model, pred, feats, extra.args){
# transform back to original value
pred$data$truth = inverse_fun(pred$data$truth)
pred$data$response = inverse_fun(pred$data$response)
return(original_measure$fun(task, model, pred, feats, extra.args))
}
transf_measure = makeMeasure(
id = 'ii', name = 'ccc',
properties = original_measure$properties,
minimize = original_measure$minimize, best = original_measure$best, worst = original_measure$worst,
fun = transf_measure_fun)
transf_measure = setAggregation(transf_measure, original_measure$aggr)
aggregated_measure = list(transf_measure, setAggregation(transf_measure, test.sd), setAggregation(transf_measure, train.mean), setAggregation(transf_measure, train.sd))
# train and predict
lrn.lm = makeLearner("regr.ksvm")
mod.lm = train(lrn.lm, bh.task)
task.pred.lm = predict(mod.lm, task = bh.task)
# inverse function on prediction
inv_pred = task.pred.lm
inv_pred$data$truth = inverse_fun(inv_pred$data$truth)
inv_pred$data$response = inverse_fun(inv_pred$data$response)
# check for performance match
performance(task.pred.lm, transf_measure)
performance(inv_pred, rmse)
# tuning
discrete_ps = makeParamSet(
makeDiscreteParam("C", values = c(0.5, 1.0, 1.5, 2.0)),
makeDiscreteParam("sigma", values = c(0.5, 1.0, 1.5, 2.0))
)
ctrl = makeTuneControlGrid()
rdesc = makeResampleDesc("CV", iters = 3L)
# this works
res = tuneParams(lrn.lm, task = bh.task, resampling = rdesc,
par.set = discrete_ps, control = ctrl, measures = transf_measure)
# try with parallelization - doesn't work
current_os = Sys.info()[['sysname']] # detect OS
if (current_os == "Windows"){
set.seed(1, "L'Ecuyer-CMRG")
parallelStart(mode = "socket", cpus = detectCores(), show.info = F)
parallel::clusterSetRNGStream(iseed = 1)
} else if (current_os == "Linux"){
set.seed(1, "L'Ecuyer-CMRG")
parallelStart(mode = "multicore", cpus = detectCores(), show.info = F)
} else {
cat('\n\n#### OS not recognized, check parallelization init\n\n')
}
res = tuneParams(lrn.lm, task = bh.task, resampling = rdesc,
par.set = discrete_ps, control = ctrl, measures = transf_measure)
parallelStop()
getting the following error:
Error in stopWithJobErrorMessages(inds, vcapply(result.list[inds], as.character)) :
Errors occurred in 16 slave jobs, displaying at most 10 of them:
00001: Error in inverse_fun(pred$data$truth) :
cannot find "inverse_fun"
I tried to pass the function with extra.args but I get an error
original_measure = eval(parse(text=tuning_criterion))
transf_measure_fun = function(task, model, pred, feats, extra.args){
# transform back to original value
pred$data$truth = extra.args$inv_fun(pred$data$truth)
pred$data$response = extra.args$inv_fun(pred$data$response)
return(original_measure$fun(task, model, pred, feats, extra.args))
}
transf_measure = makeMeasure(
id = 'ii', name = 'ccc',
properties = original_measure$properties,
minimize = original_measure$minimize, best = original_measure$best, worst = original_measure$worst,
fun = transf_measure_fun(extra.args = list(inv_fun = inverse_fun))
)
and I get
Error in FUN(X[[i]], ...) : argument "pred" is missing, with no default
Thanks in advance

Answer 1

You need to export your custom objects using parallelMap::parallelExport().
library(mlr)
#> Loading required package: ParamHelpers
library(parallelMap)
library(compiler)
# define function
inverse_fun = function(x){x^2}
inverse_fun = Vectorize(inverse_fun)
inverse_fun = cmpfun(inverse_fun, options=list(suppressUndefined=T))
assign('inverse_fun', inverse_fun, envir = .GlobalEnv)
tuning_criterion = 'rmse'
# define a new measure that applies inverse_fun to prediction and evaluates rmse
original_measure = eval(parse(text=tuning_criterion))
transf_measure_fun = function(task, model, pred, feats, extra.args){
# transform back to original value
pred$data$truth = inverse_fun(pred$data$truth)
pred$data$response = inverse_fun(pred$data$response)
return(original_measure$fun(task, model, pred, feats, extra.args))
}
transf_measure = makeMeasure(
id = 'ii', name = 'ccc',
properties = original_measure$properties,
minimize = original_measure$minimize, best = original_measure$best, worst = original_measure$worst,
fun = transf_measure_fun)
transf_measure = setAggregation(transf_measure, original_measure$aggr)
# tuning
discrete_ps = makeParamSet(
makeDiscreteParam("C", values = c(0.5, 1.0, 1.5, 2.0)),
makeDiscreteParam("sigma", values = c(0.5, 1.0, 1.5, 2.0))
)
ctrl = makeTuneControlGrid()
rdesc = makeResampleDesc("CV", iters = 3L)
lrn.lm = makeLearner("regr.ksvm")
set.seed(1, "L'Ecuyer-CMRG")
parallelStart(mode = "socket", cpus = 2, show.info = F)
parallelExport("inverse_fun", "original_measure")
res = tuneParams(lrn.lm, task = bh.task, resampling = rdesc,
par.set = discrete_ps, control = ctrl, measures = transf_measure)
#> [Tune] Started tuning learner regr.ksvm for parameter set:
#> Type len Def Constr Req Tunable Trafo
#> C discrete - - 0.5,1,1.5,2 - TRUE -
#> sigma discrete - - 0.5,1,1.5,2 - TRUE -
#> With control class: TuneControlGrid
#> Imputation value: Inf
#> [Tune] Result: C=2; sigma=0.5 : ii.test.rmse=270.8008465
parallelStop()
Created on 2019-10-08 by the reprex package (v0.3.0)
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