I want to define a function in Scala in which I can pass my training and test datasets and then it perform a simple machine learning algorithm and returns some statistics. How should do that? What will be the parameters data type?
Imagine, you need to define a function which by taking training and test datasets performs a simple classification algorithm and then return the accuracy.
What I expect to have is like as follow:
val data = MLUtils.loadLibSVMFile(sc, datadir + "/example.txt");
val splits = data.randomSplit(Array(0.6, 0.4), seed = 11L);
val training = splits(0).cache();
val test = splits(1);
val results1 = SVMFunction(training, test)
val results2 = RegressionFunction(training, test)
val results3 = ClassificationFunction(training, test)
I need just the declaration of the functions and not the code that produce the results1, results2, and results3.
def SVMFunction ("I need help here"){
//I know how to work with the training and test datasets to generate the results.
//So no need to discuss what should be here
}
Thanks.
In case you're using supervised learning you should opt for LabeledPoint. Excerpt from mllib doc:
A labeled point is a local vector, either dense or sparse, associated with a label/response. In MLlib, labeled points are used in supervised learning algorithms. We use a double to store a label, so we can use labeled points in both regression and classification. For binary classification, a label should be either 0 (negative) or 1 (positive). For multiclass classification, labels should be class indices starting from zero: 0, 1, 2, ....
And example is:
import org.apache.spark.mllib.linalg.Vectors
import org.apache.spark.mllib.regression.LabeledPoint
// Create a labeled point with a positive label and a dense feature vector.
val pos = LabeledPoint(1.0, Vectors.dense(1.0, 0.0, 3.0))
// Create a labeled point with a negative label and a sparse feature vector.
val neg = LabeledPoint(0.0, Vectors.sparse(3, Array(0, 2), Array(1.0, 3.0)))
Related
Is there a way to get the points on an ROC curve from Spark ML in pyspark? In the documentation I see an example for Scala but not python: https://spark.apache.org/docs/2.1.0/mllib-evaluation-metrics.html
Is that right? I can certainly think of ways to implement it but I have to imagine it’s faster if there’s a pre-built function. I’m working with 3 million scores and a few dozen models so speed matters.
For a more general solution that works for models besides Logistic Regression (like Decision Trees or Random Forest which lack a model summary) you can get the ROC curve using BinaryClassificationMetrics from Spark MLlib.
Note that the PySpark version doesn't implement all of the methods that the Scala version does, so you'll need to use the .call(name) function from JavaModelWrapper. It also seems that py4j doesn't support parsing scala.Tuple2 classes, so they have to be manually processed.
Example:
from pyspark.mllib.evaluation import BinaryClassificationMetrics
# Scala version implements .roc() and .pr()
# Python: https://spark.apache.org/docs/latest/api/python/_modules/pyspark/mllib/common.html
# Scala: https://spark.apache.org/docs/latest/api/java/org/apache/spark/mllib/evaluation/BinaryClassificationMetrics.html
class CurveMetrics(BinaryClassificationMetrics):
def __init__(self, *args):
super(CurveMetrics, self).__init__(*args)
def _to_list(self, rdd):
points = []
# Note this collect could be inefficient for large datasets
# considering there may be one probability per datapoint (at most)
# The Scala version takes a numBins parameter,
# but it doesn't seem possible to pass this from Python to Java
for row in rdd.collect():
# Results are returned as type scala.Tuple2,
# which doesn't appear to have a py4j mapping
points += [(float(row._1()), float(row._2()))]
return points
def get_curve(self, method):
rdd = getattr(self._java_model, method)().toJavaRDD()
return self._to_list(rdd)
Usage:
import matplotlib.pyplot as plt
# Create a Pipeline estimator and fit on train DF, predict on test DF
model = estimator.fit(train)
predictions = model.transform(test)
# Returns as a list (false positive rate, true positive rate)
preds = predictions.select('label','probability').rdd.map(lambda row: (float(row['probability'][1]), float(row['label'])))
points = CurveMetrics(preds).get_curve('roc')
plt.figure()
x_val = [x[0] for x in points]
y_val = [x[1] for x in points]
plt.title(title)
plt.xlabel(xlabel)
plt.ylabel(ylabel)
plt.plot(x_val, y_val)
BinaryClassificationMetrics in Scala implements several other useful methods as well:
metrics = CurveMetrics(preds)
metrics.get_curve('fMeasureByThreshold')
metrics.get_curve('precisionByThreshold')
metrics.get_curve('recallByThreshold')
As long as the ROC curve is a plot of FPR against TPR, you can extract the needed values as following:
your_model.summary.roc.select('FPR').collect()
your_model.summary.roc.select('TPR').collect())
Where your_model could be for example a model you got from something like this:
from pyspark.ml.classification import LogisticRegression
log_reg = LogisticRegression()
your_model = log_reg.fit(df)
Now you should just plot FPR against TPR, using for example matplotlib.
P.S.
Here is a complete example for plotting ROC curve using a model named your_model (and anything else!). I've also plot a reference "random guess" line inside the ROC plot.
import matplotlib.pyplot as plt
plt.figure(figsize=(5,5))
plt.plot([0, 1], [0, 1], 'r--')
plt.plot(your_model.summary.roc.select('FPR').collect(),
your_model.summary.roc.select('TPR').collect())
plt.xlabel('FPR')
plt.ylabel('TPR')
plt.show()
To get ROC metrics for train data (trained model), we can use your_model.summary.roc which is a DataFrame with columns FPR and TPR. See Andrea's answer.
For ROC evaluated on arbitrary test data, we can use label and probability columns to pass to sklearn's roc_curve to get FPR and TPR. Here we assume a binary classification problem where the y score is the probability of predicting 1. See also How to split Vector into columns - using PySpark, How to convert a pyspark dataframe column to numpy array
Example
from sklearn.metrics import roc_curve
model = lr.fit(train_df)
test_df_predict = model.transform(test_df)
y_score = test_df_predict.select(vector_to_array("probability")[1]).rdd.keys().collect()
y_true = test_df_predict.select("label").rdd.keys().collect()
fpr, tpr, thresholds = roc_curve(y_true, y_score)
I would like to perform KMeans using the Spark ML. Input is a libsvm dataset:
val spark = SparkSession.builder.master("local").appName("my-spark-app").getOrCreate()
// Start time
//val intial_Data=spark.read.option("header",true).csv("C://sample_lda_data.txt")
val dataset = spark.read.format("libsvm").load("C:\\spark\\data\\mllib\\sample_kmeans_data.txt")
// Trains a k-means model.
val kmeans = new KMeans().setK(2).setSeed(1L)
val model = kmeans.fit(dataset)
// Evaluate clustering by computing Within Set Sum of Squared Errors.
val WSSSE = model.computeCost(dataset)
println(s"Within Set Sum of Squared Errors = $WSSSE")
// Shows the result.
println("Cluster Centers: ")
model.clusterCenters.foreach(println)
So i would like to use a csv file and apply KMeans by the Spark ML.
I did this:
val intial_Data=spark.read.option("header",true).csv("C://sample_lda_data.txt")
val arrayCol= array(inputData.columns.drop(1).map(col).map(_.cast(DoubleType)): _*)
import spark.implicits._
// select array column and first column, and map into LabeledPoints
val result = inputData.select(col("col1").cast(DoubleType), arrayCol).map(r => LabeledPoint(r.getAs[Double](0),Vectors.dense(r.getAs[WrappedArray[Double]](1).toArray)))
// Trains a k-means model
val kmeans = new KMeans().setK(2)
val model = kmeans.fit(result)
// Evaluate clustering by computing Within Set Sum of Squared Errors.
val WSSSE = model.computeCost(dataset)
println(s"Within Set Sum of Squared Errors = $WSSSE")
// Shows the result.
println("Cluster Centers: ")
model.clusterCenters.foreach(println)
I tried to turn csv file into a Dataset[LabledPoint].
Is my transformation correct?
In spark 2 instead of MLlib , we are using ML package. Which workon dataset and ML flows work in pipeline model. What u need to do is U have to make a dataset and make two columns feature,label. feature is the a vector of features u need to feed into the algo. The other column label is the target column. To make feature column u just need to use vector assembler to assemble all the features u want to use. If you have a target colunm then rename it as label. after fitting this dataset into algo u will get your model.
Using ml, Spark 2.0 (Python) and a 1.2 million row dataset, I am trying to create a model that predicts purchase tendency with a Random Forest Classifier. However when applying the transformation to the splitted test dataset the prediction is always 0.
The dataset looks like:
[Row(tier_buyer=u'0', N1=u'1', N2=u'0.72', N3=u'35.0', N4=u'65.81', N5=u'30.67', N6=u'0.0'....
tier_buyer is the field used as a label indexer. The rest of the fields contain numeric data.
Steps
1.- Load the parquet file, and fill possible null values:
parquet = spark.read.parquet('path_to_parquet')
parquet.createOrReplaceTempView("parquet")
dfraw = spark.sql("SELECT * FROM parquet").dropDuplicates()
df = dfraw.na.fill(0)
2.- Create features vector:
features = VectorAssembler(
inputCols = ['N1','N2'...],
outputCol = 'features')
3.- Create string indexer:
label_indexer = StringIndexer(inputCol = 'tier_buyer', outputCol = 'label')
4.- Split the train and test datasets:
(train, test) = df.randomSplit([0.7, 0.3])
Resulting train dataset
Resulting Test dataset
5.- Define the classifier:
classifier = RandomForestClassifier(labelCol = 'label', featuresCol = 'features')
6.- Pipeline the stages and fit the train model:
pipeline = Pipeline(stages=[features, label_indexer, classifier])
model = pipeline.fit(train)
7.- Transform the test dataset:
predictions = model.transform(test)
8.- Output the test result, grouped by prediction:
predictions.select("prediction", "label", "features").groupBy("prediction").count().show()
As you can see, the outcome is always 0. I have tried with multiple feature variations in hopes of reducing the noise, also trying from different sources and infering the schema, with no luck and the same results.
Questions
Is the current setup, as described above, correct?
Could the null value filling on the original Dataframe be source of failure to effectively perform the prediction?
In the screenshot shown above it looks like some features are in the form of a tuple and other of a list, why? I'm guessing this could be a possible source of error. (They are representation of Dense and Sparse Vectors)
It seems your features [N1, N2, ...] are strings. You man want to cast all your features as FloatType() or something along those lines. It may be prudent to fillna() after type casting.
Reading the src of https://spark.apache.org/docs/1.5.2/ml-ann.html :
import org.apache.spark.ml.classification.MultilayerPerceptronClassifier
import org.apache.spark.ml.evaluation.MulticlassClassificationEvaluator
import org.apache.spark.mllib.util.MLUtils
import org.apache.spark.sql.Row
// Load training data
val data = MLUtils.loadLibSVMFile(sc, "data/mllib/sample_multiclass_classification_data.txt").toDF()
// Split the data into train and test
val splits = data.randomSplit(Array(0.6, 0.4), seed = 1234L)
val train = splits(0)
val test = splits(1)
// specify layers for the neural network:
// input layer of size 4 (features), two intermediate of size 5 and 4 and output of size 3 (classes)
val layers = Array[Int](4, 5, 4, 3)
// create the trainer and set its parameters
val trainer = new MultilayerPerceptronClassifier()
.setLayers(layers)
.setBlockSize(128)
.setSeed(1234L)
.setMaxIter(100)
// train the model
val model = trainer.fit(train)
// compute precision on the test set
val result = model.transform(test)
val predictionAndLabels = result.select("prediction", "label")
val evaluator = new MulticlassClassificationEvaluator()
.setMetricName("precision")
println("Precision:" + evaluator.evaluate(predictionAndLabels))
Once the model has been trained how can a new training example be classified ?
Can a new training example be added to the model where the label is not set and the classifier will try to classify this training example based on the training data ?
Why is it required that the dataframe labels are of type Double ?
Firstly, the only way to add another observation to the model is by incorporating that data point into the training data, in this case to your train variable. In order to achieve this, you can convert that point into a DataFrame (obviously of only one record) and then use the unionAll method. Nevertheless, you will have to retrain the model using this new dataset.
However, to classify observations using your model you will have to convert your unclassified data into a DataFrame with the same structure that had your training data. And then use the method transform of your model. By the way, notice that models have that method, because they are subclasses of Transformer.
Finally, you have to use Double because that is the way how the LabeledPoint class was defined. It receives a Double as label and a SparseVector or DenseVector as features. I don't know the exact motivation but in my own experience, which isn't wide, all classification and regression algorithms work with float point numbers.Furthermore, gradient descent algorithm, which is widely used to fit most models, uses numbers not letters nor classes to compute the error in each iteration.
I have a LabeledPoint on witch I want to run logistic regression:
Data: org.apache.spark.rdd.RDD[org.apache.spark.mllib.regression.LabeledPoint] =
MapPartitionsRDD[3335] at map at <console>:44
using code:
val splits = Data.randomSplit(Array(0.75, 0.25), seed = 2L)
val training = splits(0).cache()
val test = splits(1)
val numIterations = 100
val model = LogisticRegressionWithSGD.train(training, numIterations)
My problem is that I don't want to use all of the features from LabeledPoint, but only some of them. I've got a list o features that I wan't to use, for example:
LoF=List(223244,334453...
How can I get only the features that I want to use from LabeledPoint o select them in logistic regression?
Feature selection allows selecting the most relevant features for use in model construction. Feature selection reduces the size of the vector space and, in turn, the complexity of any subsequent operation with vectors. The number of features to select can be tuned using a held-out validation set.
One way to do what you are seeking is using the ElementwiseProduct.
ElementwiseProduct multiplies each input vector by a provided “weight” vector, using element-wise multiplication. In other words, it scales each column of the dataset by a scalar multiplier. This represents the Hadamard product between the input vector, v and transforming vector, w, to yield a result vector.
So if we set the weight of the features we want to keep to 1.0 and the others to 0.0, we can say that the remaining resulting features computed by the ElementwiseProduct of the original vector and the 0-1 weight vectors will select the features we need :
import org.apache.spark.mllib.feature.ElementwiseProduct
import org.apache.spark.mllib.linalg.Vectors
// Creating dummy LabeledPoint RDD
val data = sc.parallelize(Array(LabeledPoint(1.0, Vectors.dense(1.0, 0.0, 3.0,5.0,1.0)), LabeledPoint(1.0,Vectors.dense(4.0, 5.0, 6.0,1.0,2.0)),LabeledPoint(0.0,Vectors.dense(4.0, 2.0, 3.0,0.0,2.0))))
data.toDF.show
// +-----+--------------------+
// |label| features|
// +-----+--------------------+
// | 1.0|[1.0,0.0,3.0,5.0,...|
// | 1.0|[4.0,5.0,6.0,1.0,...|
// | 0.0|[4.0,2.0,3.0,0.0,...|
// +-----+--------------------+
// You'll need to know how many features you have, I have used 5 for the example
val numFeatures = 5
// The indices represent the features we want to keep
// Note : indices start with 0 so actually here you are keeping features 4 and 5.
val indices = List(3, 4).toArray
// Now we can create our weights vectors
val weights = Array.fill[Double](indices.size)(1)
// Create the sparse vector of the features we need to keep.
val transformingVector = Vectors.sparse(numFeatures, indices, weights)
// Init our vector transformer
val transformer = new ElementwiseProduct(transformingVector)
// Apply it to the data.
val transformedData = data.map(x => LabeledPoint(x.label,transformer.transform(x.features).toSparse))
transformedData.toDF.show
// +-----+-------------------+
// |label| features|
// +-----+-------------------+
// | 1.0|(5,[3,4],[5.0,1.0])|
// | 1.0|(5,[3,4],[1.0,2.0])|
// | 0.0| (5,[4],[2.0])|
// +-----+-------------------+
Note:
You noticed that I used the sparse vector representation for space optimization.
features are sparse vectors.