多类概率解释器的 Force_plot

如何解决多类概率解释器的 Force_plot

我遇到了关于 Python SHAP 库的错误。 虽然根据对数几率创建力图没有问题，但我无法根据概率创建力图。 目标是获得总和为预测概率的 base_values 和 shap_values。

这有效：

import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
import xgboost as xgb
import sklearn
import shap

X,y = shap.datasets.iris()
X_display,y_display = shap.datasets.iris(display=True)

X_train,X_test,y_train,y_test = sklearn.model_selection.train_test_split(X,y,test_size = 0.2,random_state = 42)

#fit xgboost model
params = {
    'objective': "multi:softprob",'eval_metric': "mlogloss",'num_class': 3
}

xgb_fit = xgb.train(
   params = params,dtrain = xgb.DMatrix(data = X_train,label = y_train) 
)

#create shap values and perform tests
explainer = shap.TreeExplainer(xgb_fit)
shap_values = explainer.shap_values(X_train)

这不起作用：

explainer = shap.TreeExplainer(
    model = xgb_fit,data = X_train,feature_perturbation='interventional',model_output = 'probability'
)

使用过的包：

matplotlib 3.4.1

numpy 1.20.2

熊猫 1.2.4

scikit-learn 0.24.1

形成 0.39.0

xgboost 1.4.1

解决方法

要查看多类分类的原始分数在概率空间中的累加情况，请尝试KernelExplainer：

from xgboost import XGBClassifier
from sklearn.model_selection import train_test_split
from shap import datasets,KernelExplainer,force_plot,initjs
from scipy.special import softmax,expit

initjs()

X,y = datasets.iris()
X_train,X_test,y_train,y_test = train_test_split(
    X,y,test_size=0.2,random_state=42
)
clf = XGBClassifier(random_state=42,eval_metric="mlogloss",use_label_encoder=False)
clf.fit(X_train,y_train)
ke = KernelExplainer(clf.predict_proba,data=X_train)
shap_values = ke.shap_values(X_test)

force_plot(ke.expected_value[1],shap_values[1][0],feature_names=X.columns)

健全性检查：

1. 预期结果（最多舍入误差）：

clf.predict_proba(X_test[:1])
#array([[0.0031177,0.9867134,0.01016894]],dtype=float32)

2. 基本值：

clf.predict_proba(X_train).mean(0)
#array([0.3339472,0.34133017,0.32472247],dtype=float32)

（或者如果您愿意np.unique(y_train,return_counts=True)[1]/len(y_train)）