问题
I have 7 classes and the total number of records are 115 and I wanted to run Random Forest model over this data. But as the data is not enough to get a high accuracy. So i wanted to apply oversampling over all the classes in a way that the majority class itself get higher count and then minority accordingly. Is this possible in PySpark?
+---------+-----+
| SubTribe|count|
+---------+-----+
| Chill| 10|
| Cool| 18|
|Adventure| 18|
| Quirk| 13|
| Mystery| 25|
| Party| 18|
|Glamorous| 13|
+---------+-----+
回答1:
Maybe this project can be useful for your goal: Spark SMOTE
But I think that 115 records aren't enough for a random forest. You can use other simplest technique like decision trees
You can check this answer:
Is Random Forest suitable for very small data sets?
回答2:
Here is another implementation of Pyspark and Scala smote that I have used in the past. I have copped the code across and referenced the source because its quite small:
Pyspark:
import random
import numpy as np
from pyspark.sql import Row
from sklearn import neighbors
from pyspark.ml.feature import VectorAssembler
def vectorizerFunction(dataInput, TargetFieldName):
if(dataInput.select(TargetFieldName).distinct().count() != 2):
raise ValueError("Target field must have only 2 distinct classes")
columnNames = list(dataInput.columns)
columnNames.remove(TargetFieldName)
dataInput = dataInput.select((','.join(columnNames)+','+TargetFieldName).split(','))
assembler=VectorAssembler(inputCols = columnNames, outputCol = 'features')
pos_vectorized = assembler.transform(dataInput)
vectorized = pos_vectorized.select('features',TargetFieldName).withColumn('label',pos_vectorized[TargetFieldName]).drop(TargetFieldName)
return vectorized
def SmoteSampling(vectorized, k = 5, minorityClass = 1, majorityClass = 0, percentageOver = 200, percentageUnder = 100):
if(percentageUnder > 100|percentageUnder < 10):
raise ValueError("Percentage Under must be in range 10 - 100");
if(percentageOver < 100):
raise ValueError("Percentage Over must be in at least 100");
dataInput_min = vectorized[vectorized['label'] == minorityClass]
dataInput_maj = vectorized[vectorized['label'] == majorityClass]
feature = dataInput_min.select('features')
feature = feature.rdd
feature = feature.map(lambda x: x[0])
feature = feature.collect()
feature = np.asarray(feature)
nbrs = neighbors.NearestNeighbors(n_neighbors=k, algorithm='auto').fit(feature)
neighbours = nbrs.kneighbors(feature)
gap = neighbours[0]
neighbours = neighbours[1]
min_rdd = dataInput_min.drop('label').rdd
pos_rddArray = min_rdd.map(lambda x : list(x))
pos_ListArray = pos_rddArray.collect()
min_Array = list(pos_ListArray)
newRows = []
nt = len(min_Array)
nexs = percentageOver/100
for i in range(nt):
for j in range(nexs):
neigh = random.randint(1,k)
difs = min_Array[neigh][0] - min_Array[i][0]
newRec = (min_Array[i][0]+random.random()*difs)
newRows.insert(0,(newRec))
newData_rdd = sc.parallelize(newRows)
newData_rdd_new = newData_rdd.map(lambda x: Row(features = x, label = 1))
new_data = newData_rdd_new.toDF()
new_data_minor = dataInput_min.unionAll(new_data)
new_data_major = dataInput_maj.sample(False, (float(percentageUnder)/float(100)))
return new_data_major.unionAll(new_data_minor)
dataInput = spark.read.format('csv').options(header='true',inferSchema='true').load("sam.csv").dropna()
SmoteSampling(vectorizerFunction(dataInput, 'Y'), k = 2, minorityClass = 1, majorityClass = 0, percentageOver = 90, percentageUnder = 5)
Scala:
// Import the necessary packages
import org.apache.spark.ml.feature.BucketedRandomProjectionLSH
import org.apache.spark.ml.feature.VectorAssembler
import org.apache.spark.sql.expressions.Window
import org.apache.spark.mllib.linalg.Vectors
import org.apache.spark.sql.functions.rand
import org.apache.spark.sql.functions._
object smoteClass{
def KNNCalculation(
dataFinal:org.apache.spark.sql.DataFrame,
feature:String,
reqrows:Int,
BucketLength:Int,
NumHashTables:Int):org.apache.spark.sql.DataFrame = {
val b1 = dataFinal.withColumn("index", row_number().over(Window.partitionBy("label").orderBy("label")))
val brp = new BucketedRandomProjectionLSH().setBucketLength(BucketLength).setNumHashTables(NumHashTables).setInputCol(feature).setOutputCol("values")
val model = brp.fit(b1)
val transformedA = model.transform(b1)
val transformedB = model.transform(b1)
val b2 = model.approxSimilarityJoin(transformedA, transformedB, 2000000000.0)
require(b2.count > reqrows, println("Change bucket lenght or reduce the percentageOver"))
val b3 = b2.selectExpr("datasetA.index as id1",
"datasetA.feature as k1",
"datasetB.index as id2",
"datasetB.feature as k2",
"distCol").filter("distCol>0.0").orderBy("id1", "distCol").dropDuplicates().limit(reqrows)
return b3
}
def smoteCalc(key1: org.apache.spark.ml.linalg.Vector, key2: org.apache.spark.ml.linalg.Vector)={
val resArray = Array(key1, key2)
val res = key1.toArray.zip(key2.toArray.zip(key1.toArray).map(x => x._1 - x._2).map(_*0.2)).map(x => x._1 + x._2)
resArray :+ org.apache.spark.ml.linalg.Vectors.dense(res)}
def Smote(
inputFrame:org.apache.spark.sql.DataFrame,
feature:String,
label:String,
percentOver:Int,
BucketLength:Int,
NumHashTables:Int):org.apache.spark.sql.DataFrame = {
val groupedData = inputFrame.groupBy(label).count
require(groupedData.count == 2, println("Only 2 labels allowed"))
val classAll = groupedData.collect()
val minorityclass = if (classAll(0)(1).toString.toInt > classAll(1)(1).toString.toInt) classAll(1)(0).toString else classAll(0)(0).toString
val frame = inputFrame.select(feature,label).where(label + " == " + minorityclass)
val rowCount = frame.count
val reqrows = (rowCount * (percentOver/100)).toInt
val md = udf(smoteCalc _)
val b1 = KNNCalculation(frame, feature, reqrows, BucketLength, NumHashTables)
val b2 = b1.withColumn("ndtata", md($"k1", $"k2")).select("ndtata")
val b3 = b2.withColumn("AllFeatures", explode($"ndtata")).select("AllFeatures").dropDuplicates
val b4 = b3.withColumn(label, lit(minorityclass).cast(frame.schema(1).dataType))
return inputFrame.union(b4).dropDuplicates
}
}
- Source
来源：https://stackoverflow.com/questions/53936850/oversampling-or-smote-in-pyspark