SVM 尚未使用 `probability = TRUE` 进行训练,概率不可用于预测

SVM has not been trained using `probability = TRUE`, probabilities not available for predictions

我在尝试使用 mlr3 输出 SVM 的预测概率时遇到问题。

library(mlr3)
task = mlr_tasks$get("iris")
svm_learner = mlr_learners$get("classif.svm")
train_set = sample(task$nrow, 0.8 * task$nrow)
test_set = setdiff(seq_len(task$nrow), train_set)

svm_learner$train(task, row_ids = task$row_ids[train_set])
svm_learner$predict_type<-"prob"
prediction<-svm_learner$predict(task,row_ids = task$row_ids[test_set])
prediction
Warning message:
In predict.svm(self$model, newdata = newdata, probability = (self$predict_type ==  :
  SVM has not been trained using `probability = TRUE`, probabilities not available for predictions.



Session info
> sessionInfo(package = NULL)
R version 3.6.2 (2019-12-12)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 17763)

Matrix products: default

Random number generation:
 RNG:     Mersenne-Twister 
 Normal:  Inversion 
 Sample:  Rounding 

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

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

other attached packages:
 [1] precrec_0.10.1     forcats_0.4.0      stringr_1.4.0      purrr_0.3.3        readr_1.3.1       
 [6] tidyr_1.0.0        tibble_2.1.3       tidyverse_1.2.1    dplyr_0.8.3        mlr3learners_0.1.5
[11] GGally_1.4.0       ggplot2_3.2.1      mlr3_0.1.6         mlr3viz_0.1.0      e1071_1.7-3       
[16] biomaRt_2.38.0    

loaded via a namespace (and not attached):
 [1] Biobase_2.42.0       httr_1.4.1           bit64_0.9-7          jsonlite_1.6        
 [5] modelr_0.1.4         assertthat_0.2.1     lgr_0.3.3            stats4_3.6.2        
 [9] blob_1.2.0           cellranger_1.1.0     mlr3misc_0.1.6       progress_1.2.2      
[13] pillar_1.4.3         RSQLite_2.1.2        backports_1.1.5      lattice_0.20-38     
[17] glue_1.3.1           uuid_0.1-2           digest_0.6.23        RColorBrewer_1.1-2  
[21] checkmate_1.9.4      rvest_0.3.3          colorspace_1.4-1     plyr_1.8.5          
[25] XML_3.98-1.20        pkgconfig_2.0.3      mlr3measures_0.1.1   broom_0.5.2         
[29] haven_2.1.0          scales_1.0.0         generics_0.0.2       IRanges_2.16.0      
[33] withr_2.1.2          BiocGenerics_0.28.0  lazyeval_0.2.2       cli_2.0.0           
[37] magrittr_1.5         crayon_1.3.4         readxl_1.3.1         paradox_0.1.0       
[41] memoise_1.1.0        fansi_0.4.0          nlme_3.1-142         xml2_1.2.0          
[45] class_7.3-15         tools_3.6.2          data.table_1.12.8    prettyunits_1.0.2   
[49] hms_0.5.2            lifecycle_0.1.0      S4Vectors_0.20.1     munsell_0.5.0       
[53] AnnotationDbi_1.44.0 compiler_3.6.2       rlang_0.4.1          grid_3.6.2          
[57] RCurl_1.95-4.12      rstudioapi_0.10      bitops_1.0-6         labeling_0.3        
[61] gtable_0.3.0         DBI_1.0.0            reshape_0.8.8        reshape2_1.4.3      
[65] R6_2.4.1             lubridate_1.7.4      bit_1.1-14           zeallot_0.1.0       
[69] stringi_1.4.3        parallel_3.6.2       Rcpp_1.0.2           vctrs_0.2.1         
[73] tidyselect_0.2.5

我了解SVM不会输出概率,但是SVM可以将预测数据拟合到分离超平面函数,并从超平面得到带符号的距离度量。我想检索带符号的距离,然后用它们来计算 AUC。 但是对于 predict_type<-"response",我只能得到预测的 class,而不是符号距离。使用 predict_type<-"probability",我得到了上面的错误。

您的代码是倒退的。修改如下:

library(mlr3)
task = mlr_tasks$get("iris")
svm_learner = mlr_learners$get("classif.svm")
train_set = sample(task$nrow, 0.8 * task$nrow)
test_set = setdiff(seq_len(task$nrow), train_set)


svm_learner$predict_type<-"prob"
svm_learner$train(task, row_ids = task$row_ids[train_set])
prediction<-svm_learner$predict(task,row_ids = task$row_ids[test_set])
prediction

注意改变predict_type然后训练。