PySpark_Ml_逻辑归回分词预测

Llib是Spark的机器学习库，包括以下主要功能。

实用工具：线性代数，统计，数据处理等工具
特征工程：特征提取，特征转换，特征选择
常用算法：分类，回归，聚类，协同过滤，降维
模型优化：模型评估，参数优化。

MLlib库包括两个不同的部分：

pyspark.mllib 包含基于rdd的机器学习算法API，目前不再更新，以后将被丢弃，不建议使用。

pyspark.ml 包含基于DataFrame的机器学习算法API，可以用来构建机器学习工作流Pipeline，推荐使用。

一，MLlib基本概念

DataFrame:
MLlib中数据的存储形式，其列可以存储特征向量，标签,以及原始的文本，图像。

Transformer：
转换器。具有transform方法。通过附加一个或多个列将一个DataFrame转换成另外一个DataFrame。

Estimator：估计器。具有fit方法。它接受一个DataFrame数据作为输入后经过训练，产生一个转换器Transformer。

Pipeline：流水线。具有setStages方法。顺序将多个Transformer和1个Estimator串联起来，得到一个流水线模型。

二， Pipeline流水线范例

任务描述：用逻辑回归模型预测句子中是否包括”spark“这个单词。

from pyspark.ml.feature import Tokenizer,HashingTF
from pyspark.ml.classification import LogisticRegression
from pyspark.ml.evaluation import MulticlassClassificationEvaluator,BinaryClassificationEvaluator
from pyspark.ml import Pipeline,PipelineModel
from pyspark.ml.linalg import Vector
from pyspark.sql import Row

1，准备数据

dftrain = spark.createDataFrame([(0,"a b c d e spark",1.0),
                (1,"a c f",0.0),
                (2,"spark hello world",1.0),
                (3,"hadoop mapreduce",0.0),
                (4,"I love spark", 1.0),
                (5,"big data",0.0)],["id","text","label"])
dftrain.show()

+---+-----------------+-----+
| id|             text|label|
+---+-----------------+-----+
|  0|  a b c d e spark|  1.0|
|  1|            a c f|  0.0|
|  2|spark hello world|  1.0|
|  3| hadoop mapreduce|  0.0|
|  4|     I love spark|  1.0|
|  5|         big data|  0.0|
+---+-----------------+-----+

2，定义模型

tokenizer = Tokenizer().setInputCol("text").setOutputCol("words")
print(type(tokenizer))

hashingTF = HashingTF().setNumFeatures(100) \
   .setInputCol(tokenizer.getOutputCol()) \
   .setOutputCol("features")
print(type(hashingTF))

lr = LogisticRegression().setLabelCol("label")
#print(lr.explainParams)
lr.setFeaturesCol("features").setMaxIter(10).setRegParam(0.2)
print(type(lr))

pipe = Pipeline().setStages([tokenizer,hashingTF,lr])
print(type(pipe))     

<class 'pyspark.ml.feature.Tokenizer'>
<class 'pyspark.ml.feature.HashingTF'>
<class 'pyspark.ml.classification.LogisticRegression'>
<class 'pyspark.ml.pipeline.Pipeline'>

3，训练模型

model = pipe.fit(dftrain)
print(type(model))

<class 'pyspark.ml.pipeline.PipelineModel'>

4，使用模型

dftest = spark.createDataFrame([(7,"spark job",1.0),(9,"hello world",0.0),
                 (10,"a b c d e",0.0),(11,"you can you up",0.0),
                (12,"spark is easy to use.",1.0)]).toDF("id","text","label")
dftest.show()

dfresult = model.transform(dftest)

dfresult.selectExpr("text","features","probability","prediction").show()

+---+--------------------+-----+
| id|                text|label|
+---+--------------------+-----+
|  7|           spark job|  1.0|
|  9|         hello world|  0.0|
| 10|           a b c d e|  0.0|
| 11|      you can you up|  0.0|
| 12|spark is easy to ...|  1.0|
+---+--------------------+-----+

+--------------------+--------------------+--------------------+----------+
|                text|            features|         probability|prediction|
+--------------------+--------------------+--------------------+----------+
|           spark job|(100,[57,86],[1.0...|[0.30134853865356...|       1.0|
|         hello world|(100,[60,89],[1.0...|[0.20714372651040...|       1.0|
|           a b c d e|(100,[50,65,67,68...|[0.24502686265469...|       1.0|
|      you can you up|(100,[33,38,51],[...|[0.87589306761045...|       0.0|
|spark is easy to ...|(100,[9,21,60,86,...|[0.07662944406376...|       1.0|
+--------------------+--------------------+--------------------+----------+

5，评估模型

dfresult.printSchema()

root
 |-- id: long (nullable = true)
 |-- text: string (nullable = true)
 |-- label: double (nullable = true)
 |-- words: array (nullable = true)
 |    |-- element: string (containsNull = true)
 |-- features: vector (nullable = true)
 |-- rawPrediction: vector (nullable = true)
 |-- probability: vector (nullable = true)
 |-- prediction: double (nullable = false)

evaluator = MulticlassClassificationEvaluator().setMetricName("f1") \
    .setPredictionCol("prediction").setLabelCol("label")

#print(evaluator.explainParams())
accuracy  = evaluator.evaluate(dfresult)
print("\n accuracy = {}".format(accuracy))

accuracy = 0.5666666666666667

6，保存模型

#可以将训练好的模型保存到磁盘中
model.write().overwrite().save("./data/mymodel.model")

#也可以将没有训练的模型保存到磁盘中
#pipeline.write.overwrite().save("./data/unfit-lr-model")

#重新载入模型
model_loaded = PipelineModel.load("./data/mymodel.model")
model_loaded.transform(dftest).select("text","label","prediction").show()

+--------------------+-----+----------+
|                text|label|prediction|
+--------------------+-----+----------+
|           spark job|  1.0|       1.0|
|         hello world|  0.0|       1.0|
|           a b c d e|  0.0|       1.0|
|      you can you up|  0.0|       0.0|
|spark is easy to ...|  1.0|       1.0|
+--------------------+-----+----------+