在进行数值编码时出现错误,怎么解决？

'Device_Type','Filled_Form','Gender','Var1','Var2','Mobile_Verified','Source'这些特征类型为object

# 数值编码
from sklearn.preprocessing import LabelEncoder
le = LabelEncoder()
var_to_encode = ['Device_Type','Filled_Form','Gender','Var1','Var2','Mobile_Verified','Source']
for col in var_to_encode:
    data[col] = le.fit_transform(data[col])

错误代码：

TypeError: '<' not supported between instances of 'float' and 'str'