When building complex models, it is often difficult to explain why
the model should be trusted. While global measures such as accuracy are
useful, they cannot be used for explaining why a model made a specific
prediction. 'lime' (a port of the 'lime' 'Python' package) is a method for
explaining the outcome of black box models by fitting a local model around
the point in question an perturbations of this point. The approach is
described in more detail in the article by Ribeiro et al. (2016)
Whose models were simply sublime,
It gave explanations for their variations,
one observation at a time.
lime-rick by Mara Averick
This is an R port of the Python lime package (https://github.com/marcotcr/lime) developed by the authors of the lime (Local Interpretable Model-agnostic Explanations) approach for black-box model explanations. All credits for the invention of the approach goes to the original developers.
The purpose of
lime is to explain the predictions of black box
classifiers. What this means is that for any given prediction and any
given classifier it is able to determine a small set of features in the
original data that has driven the outcome of the prediction. To learn
more about the methodology of
lime read the
paper and visit the repository of
the original implementation.
lime package for R does not aim to be a line-by-line port of its
Python counterpart. Instead it takes the ideas laid out in the original
code and implements them in an API that is idiomatic to R.
Out of the box
lime supports a long range of models, e.g. those
created with caret, parsnip, and mlr. Support for unsupported models are
easy to achieve by adding a
model_type method for
the given model.
The following shows how a random forest model is trained on the iris
data set and how
lime is then used to explain a set of new
library(caret)library(lime)# Split up the data setiris_test <- iris[1:5, 1:4]iris_train <- iris[-(1:5), 1:4]iris_lab <- iris[][-(1:5)]# Create Random Forest model on iris datamodel <- train(iris_train, iris_lab, method = 'rf')# Create an explainer objectexplainer <- lime(iris_train, model)# Explain new observationexplanation <- explain(iris_test, explainer, n_labels = 1, n_features = 2)# The output is provided in a consistent tabular format and includes the# output from the model.explanation#> # tibble [10 × 13]#> model_type case label label_prob model_r2 model_intercept#> <chr> <chr> <chr> <dbl> <dbl> <dbl>#> 1 classific… 1 seto… 1 0.340 0.263#> 2 classific… 1 seto… 1 0.340 0.263#> 3 classific… 2 seto… 1 0.336 0.259#> 4 classific… 2 seto… 1 0.336 0.259#> 5 classific… 3 seto… 1 0.361 0.258#> 6 classific… 3 seto… 1 0.361 0.258#> 7 classific… 4 seto… 1 0.364 0.247#> 8 classific… 4 seto… 1 0.364 0.247#> 9 classific… 5 seto… 1 0.343 0.256#> 10 classific… 5 seto… 1 0.343 0.256#> # ... with 7 more variables: model_prediction <dbl>, feature <chr>,#> # feature_value <dbl>, feature_weight <dbl>, feature_desc <chr>,#> # data <list>, prediction <list># And can be visualised directlyplot_features(explanation)
lime also supports explaining image and text models. For image
explanations the relevant areas in an image can be highlighted:
explanation <- .load_image_example()plot_image_explanation(explanation)
Here we see that the second most probably class is hardly true, but is due to the model picking up waxy areas of the produce and interpreting them as wax-light surface.
For text the explanation can be shown by highlighting the important
words. It even includes a
shiny application for interactively
exploring text models:
lime is available on CRAN and can be installed using the standard
To get the development version, install from GitHub instead:
as_regressor()for ad-hoc specification of the model type in case the heuristic implemented in
as_classifier()also lets you add/overwrite the class labels.
goweras the new default similarity measure for tabular data
bin_continuous = FALSEthe default behavior is now to sample from a kernel density estimation rather than assume a normal distribution.
plot_text_explanation()with better formatting and scrolling support for many explanations
NEWS.mdfile to track changes to the package.
POSIXtcolumns. They will be kept constant during permutations so that
limewill explain the model behaviour at the given timepoint based on the remaining features (#39).
plot_explanations()for an overview plot of a large explanation set