Pandas中的幻象错误

Question

我把所有的分类字符串值都转换成了数字，而且我确信没有空值。 我的数据集：https://www.kaggle.com/murderaccountability/homicide-reports/data我的代码：

import numpy as np # linear algebra
import pandas as pd # data processing, CSV file I/O (e.g. pd.read_csv)
from pandas import DataFrame
from sklearn.model_selection import train_test_split
from sklearn.neighbors import KNeighborsClassifier
database_df = pd.read_csv("database.csv",low_memory=False,usecols=  ['State','Year','Month','Crime Type','Crime Solved','Victim Sex','Victim Age','Victim Race','Perpetrator Sex','Perpetrator Age','Perpetrator Race','Relationship','Weapon','Victim Count','Perpetrator Count'])
database_df.replace({'Victim Sex':mappingGender,'Perpetrator    
Sex':mappingGender},inplace=True)
database_df.replace({'Crime Solved':mappingCrimeSolved},inplace=True)
database_df.replace({'Victim Race':mappingRace,'Perpetrator  
Race':mappingRace},inplace=True)
database_df.replace({'Relationship':mappingRelation},inplace=True)
database_df.replace({'Weapon':mappingWeapon},inplace=True)
database_df.replace({'Crime Type':mappingCrimeType},inplace=True)
database_df.replace({'State':mappingState},inplace=True)
database_df.replace({'Month':mappingMonth},inplace=True)

X, y = database_df.iloc[:,:-1], database_df.iloc[:, -1]
X_train, X_test, y_train, y_test = train_test_split(X, y,test_size=0.3, random_state=42) 
knn = KNeighborsClassifier(n_neighbors=8)
knn.fit(X_train,y_train)
knn.predict(X_test)

**我得到这个错误** ValueError:无法将字符串转换为浮点值：

求你了，我需要帮助！没有字符串指向错误