我有一个LIBSVM缩放模型（使用svm-scale生成），我想将其移植到PySpark。我天真地尝试了以下方法：
scaler_path = "path to model"
a = MinMaxScaler().load(scaler_path)
但我发出错误，期待一个元数据目录：
Py4JJavaErrorTraceback (most recent call last)
<ipython-input-22-1942e7522174> in <module>()
----> 1 a = MinMaxScaler().load(scaler_path)
/srv/data/spark/spark-2.0.0-bin-hadoop2.6/python/pyspark/ml/util.pyc in load(cls, path)
226 def load(cls, path):
227 """Reads an ML instance from the input path, a shortcut of `read().load(path)`."""
--> 228 return cls.read().load(path)
229
230
/srv/data/spark/spark-2.0.0-bin-hadoop2.6/python/pyspark/ml/util.pyc in load(self, path)
174 if not isinstance(path, basestring):
175 raise TypeError("path should be a basestring, got type %s" % type(path))
--> 176 java_obj = self._jread.load(path)
177 if not hasattr(self._clazz, "_from_java"):
178 raise NotImplementedError("This Java ML type cannot be loaded into Python currently: %r"
/usr/local/lib/python2.7/dist-packages/py4j/java_gateway.pyc in __call__(self, *args)
1131 answer = self.gateway_client.send_command(command)
1132 return_value = get_return_value(
-> 1133 answer, self.gateway_client, self.target_id, self.name)
1134
1135 for temp_arg in temp_args:
/srv/data/spark/spark-2.0.0-bin-hadoop2.6/python/pyspark/sql/utils.pyc in deco(*a, **kw)
61 def deco(*a, **kw):
62 try:
---> 63 return f(*a, **kw)
64 except py4j.protocol.Py4JJavaError as e:
65 s = e.java_exception.toString()
/usr/local/lib/python2.7/dist-packages/py4j/protocol.pyc in get_return_value(answer, gateway_client, target_id, name)
317 raise Py4JJavaError(
318 "An error occurred while calling {0}{1}{2}.\n".
--> 319 format(target_id, ".", name), value)
320 else:
321 raise Py4JError(
Py4JJavaError: An error occurred while calling o321.load.
: org.apache.hadoop.mapred.InvalidInputException: Input path does not exist: file:[filename]/metadata
```
是否有一个简单的解决方法来加载它？ LIBSVM模型的格式是
x
0 1
1 -1050 1030
2 0 1
3 0 3
4 0 1
5 0 1
答案 0 :(得分：6)
首先，提供的文件不是libsvm格式。 libsvm文件的正确格式如下：
<label> <index1>:<value1> <index2>:<value2> ... <indexN>:<valueN>
因此，您的数据准备工作不正确。
其次，您与load(path)一起使用的类方法MinMaxScaler从输入路径读取ML实例。
请记住： MinMaxScaler计算数据集的摘要统计信息并生成MinMaxScalerModel。然后，模型可以单独转换每个特征，使其处于给定范围内。
例如：
from pyspark.ml.linalg import Vectors
from pyspark.mllib.regression import LabeledPoint
from pyspark.ml.feature import MinMaxScaler
df = spark.createDataFrame([(1.1, Vectors.sparse(3, [(0, 1.23), (2, 4.56)])) ,(0.0, Vectors.dense([1.01, 2.02, 3.03]))],['label','features'])
df.show(truncate=False)
# +-----+---------------------+
# |label|features |
# +-----+---------------------+
# |1.1 |(3,[0,2],[1.23,4.56])|
# |0.0 |[1.01,2.02,3.03] |
# +-----+---------------------+
mmScaler = MinMaxScaler(inputCol="features", outputCol="scaled")
temp_path = "/tmp/spark/"
minMaxScalerPath = temp_path + "min-max-scaler"
mmScaler.save(minMaxScalerPath)
上面的代码段将保存MinMaxScaler要素变换器，以便在使用类方法加载后加载它。
现在，让我们来看看究竟发生了什么。类方法save将创建以下文件结构：
/tmp/spark/
└── min-max-scaler
└── metadata
├── part-00000
└── _SUCCESS
让我们检查一下part-0000文件的内容：
$ cat /tmp/spark/min-max-scaler/metadata/part-00000 | python -m json.tool
{
"class": "org.apache.spark.ml.feature.MinMaxScaler",
"paramMap": {
"inputCol": "features",
"max": 1.0,
"min": 0.0,
"outputCol": "scaled"
},
"sparkVersion": "2.0.0",
"timestamp": 1480501003244,
"uid": "MinMaxScaler_42e68455a929c67ba66f"
}
实际上当你加载变压器时：
loadedMMScaler = MinMaxScaler.load(minMaxScalerPath)
您实际上正在加载该文件。 它不会使用libsvm文件！
现在，您可以应用变换器来创建模型并转换DataFrame：
model = loadedMMScaler.fit(df)
model.transform(df).show(truncate=False)
# +-----+---------------------+-------------+
# |label|features |scaled |
# +-----+---------------------+-------------+
# |1.1 |(3,[0,2],[1.23,4.56])|[1.0,0.0,1.0]|
# |0.0 |[1.01,2.02,3.03] |[0.0,1.0,0.0]|
# +-----+---------------------+-------------+
现在让我们回到那个libsvm文件，让我们创建一些虚拟数据并使用MLUtils将其保存为libsvm格式
from pyspark.mllib.regression import LabeledPoint
from pyspark.mllib.linalg import Vectors
from pyspark.mllib.util import MLUtils
data = sc.parallelize([LabeledPoint(1.1, Vectors.sparse(3, [(0, 1.23), (2, 4.56)])), LabeledPoint(0.0, Vectors.dense([1.01, 2.02, 3.03]))])
MLUtils.saveAsLibSVMFile(data, temp_path + "data")
返回我们的文件结构：
/tmp/spark/
├── data
│ ├── part-00000
│ ├── part-00001
│ ├── part-00002
│ ├── part-00003
│ ├── part-00004
│ ├── part-00005
│ ├── part-00006
│ ├── part-00007
│ └── _SUCCESS
└── min-max-scaler
└── metadata
├── part-00000
└── _SUCCESS
您现在可以检查libsvm格式的文件内容：
$ cat /tmp/spark/data/part-0000*
1.1 1:1.23 3:4.56
0.0 1:1.01 2:2.02 3:3.03
现在让我们加载这些数据并应用：
loadedData = MLUtils.loadLibSVMFile(sc, temp_path + "data")
loadedDataDF = spark.createDataFrame(loadedData.map(lambda lp : (lp.label, lp.features.asML())), ['label','features'])
loadedDataDF.show(truncate=False)
# +-----+----------------------------+
# |label|features |
# +-----+----------------------------+
# |1.1 |(3,[0,2],[1.23,4.56]) |
# |0.0 |(3,[0,1,2],[1.01,2.02,3.03])|
# +-----+----------------------------+
注意将MLlib Vectors转换为ML Vectors非常重要。您可以阅读更多相关信息here。
model.transform(loadedDataDF).show(truncate=False)
# +-----+----------------------------+-------------+
# |label|features |scaled |
# +-----+----------------------------+-------------+
# |1.1 |(3,[0,2],[1.23,4.56]) |[1.0,0.0,1.0]|
# |0.0 |(3,[0,1,2],[1.01,2.02,3.03])|[0.0,1.0,0.0]|
# +-----+----------------------------+-------------+
我希望这能回答你的问题！