如何使用pyspark中的MultiClassMetrics计算f-分数？

Question

正如我在pyspark文档中看到的，fmeasure()函数接受两个参数，即label和{}：

fMeasure(label=None, beta=None)

什么是beta？在

我使用的是RDD中的一个非常简单的数据集： （在dataframe中，但我将其转换为RDD）

^{pr2}$

当我运行这个命令时：

multi_metrics = MulticlassMetrics(rdd)
print 'fMeasure: ', multi_metrics.fMeasure(1)

我得到这个错误：

print 'fMeasure: ', multi_metrics.fMeasure(1)
  File "/usr/hdp/current/spark-client/python/pyspark/mllib/evaluation.py", line 259, in fMeasure
    return self.call("fMeasure", label)
  File "/usr/hdp/current/spark-client/python/pyspark/mllib/common.py", line 146, in call
    return callJavaFunc(self._sc, getattr(self._java_model, name), *a)
  File "/usr/hdp/current/spark-client/python/pyspark/mllib/common.py", line 123, in callJavaFunc
    return _java2py(sc, func(*args))
  File "/usr/hdp/current/spark-client/python/lib/py4j-0.9-src.zip/py4j/java_gateway.py", line 813, in __call__
    answer, self.gateway_client, self.target_id, self.name)
  File "/usr/hdp/current/spark-client/python/pyspark/sql/utils.py", line 45, in deco
    return f(*a, **kw)
  File "/usr/hdp/current/spark-client/python/lib/py4j-0.9-src.zip/py4j/protocol.py", line 312, in get_return_value
    format(target_id, ".", name, value))
Py4JError: An error occurred while calling o154.fMeasure. Trace:
py4j.Py4JException: Method fMeasure([class java.lang.Integer]) does not exist
    at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:335)
    at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:344)
    at py4j.Gateway.invoke(Gateway.java:252)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:209)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

What is beta here?

Spark的MulticlassMetrics实现了$F{\beta}$-measure，如果将$\beta$=1，则与传统的F-measure一致。$\beta$参数允许control relative contributions of precision vs recall in F-measure。在

关于错误：如果查看实现，它实际上需要一个Double。这是fMeasure方法的pyspark包装器，这是实际的implementation（在Scala中）。在

所以你应该这样称呼它，例如：

multi_metrics = MulticlassMetrics(rdd)
print 'fMeasure: ', multi_metrics.fMeasure(1.0,1.0)