Tokenizer(分詞器)
算法介紹:
Tokenization将文本劃分為獨立個體(通常為單詞)。下面的例子展示了如何把句子劃分為單詞。
RegexTokenizer基于正規表達式提供更多的劃分選項。預設情況下,參數“pattern”為劃分文本的分隔符。或者,使用者可以指定參數“gaps”來指明正則“patten”表示“tokens”而不是分隔符,這樣來為分詞結果找到所有可能比對的情況。
示例調用:
Scala:
import org.apache.spark.ml.feature.{RegexTokenizer, Tokenizer}
val sentenceDataFrame = spark.createDataFrame(Seq(
(0, "Hi I heard about Spark"),
(1, "I wish Java could use case classes"),
(2, "Logistic,regression,models,are,neat")
)).toDF("label", "sentence")
val tokenizer = new Tokenizer().setInputCol("sentence").setOutputCol("words")
val regexTokenizer = new RegexTokenizer()
.setInputCol("sentence")
.setOutputCol("words")
.setPattern("\\W") // alternatively .setPattern("\\w+").setGaps(false)
val tokenized = tokenizer.transform(sentenceDataFrame)
tokenized.select("words", "label").take(3).foreach(println)
val regexTokenized = regexTokenizer.transform(sentenceDataFrame)
regexTokenized.select("words", "label").take(3).foreach(println)
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.RegexTokenizer;
import org.apache.spark.ml.feature.Tokenizer;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
List<Row> data = Arrays.asList(
RowFactory.create(0, "Hi I heard about Spark"),
RowFactory.create(1, "I wish Java could use case classes"),
RowFactory.create(2, "Logistic,regression,models,are,neat")
);
StructType schema = new StructType(new StructField[]{
new StructField("label", DataTypes.IntegerType, false, Metadata.empty()),
new StructField("sentence", DataTypes.StringType, false, Metadata.empty())
});
Dataset<Row> sentenceDataFrame = spark.createDataFrame(data, schema);
Tokenizer tokenizer = new Tokenizer().setInputCol("sentence").setOutputCol("words");
Dataset<Row> wordsDataFrame = tokenizer.transform(sentenceDataFrame);
for (Row r : wordsDataFrame.select("words", "label").takeAsList(3)) {
java.util.List<String> words = r.getList(0);
for (String word : words) System.out.print(word + " ");
System.out.println();
}
RegexTokenizer regexTokenizer = new RegexTokenizer()
.setInputCol("sentence")
.setOutputCol("words")
.setPattern("\\W"); // alternatively .setPattern("\\w+").setGaps(false);
Python:
from pyspark.ml.feature import Tokenizer, RegexTokenizer
sentenceDataFrame = spark.createDataFrame([
(0, "Hi I heard about Spark"),
(1, "I wish Java could use case classes"),
(2, "Logistic,regression,models,are,neat")
], ["label", "sentence"])
tokenizer = Tokenizer(inputCol="sentence", outputCol="words")
wordsDataFrame = tokenizer.transform(sentenceDataFrame)
for words_label in wordsDataFrame.select("words", "label").take(3):
print(words_label)
regexTokenizer = RegexTokenizer(inputCol="sentence", outputCol="words", pattern="\\W")
# alternatively, pattern="\\w+", gaps(False)
StopWordsRemover
算法介紹:
停用詞為在文檔中頻繁出現,但未承載太多意義的詞語,他們不應該被包含在算法輸入中。
StopWordsRemover的輸入為一系列字元串(如分詞器輸出),輸出中删除了所有停用詞。停用詞表由stopWords參數提供。一些語言的預設停用詞表可以通過StopWordsRemover.loadDefaultStopWords(language)調用。布爾參數caseSensitive指明是否區分大小寫(預設為否)。
示例:
假設我們有如下DataFrame,有id和raw兩列:
id | raw
----|----------
0 | [I,saw, the, red, baloon]
1 |[Mary, had, a, little, lamb]
通過對raw列調用StopWordsRemover,我們可以得到篩選出的結果列如下:
id | raw | filtered
----|-----------------------------|--------------------
0 | [I,saw, the, red, baloon] | [saw, red, baloon]
1 |[Mary, had, a, little, lamb]|[Mary, little, lamb]
其中,“I”, “the”, “had”以及“a”被移除。
示例調用:
Scala:
import org.apache.spark.ml.feature.StopWordsRemover
val remover = new StopWordsRemover()
.setInputCol("raw")
.setOutputCol("filtered")
val dataSet = spark.createDataFrame(Seq(
(0, Seq("I", "saw", "the", "red", "baloon")),
(1, Seq("Mary", "had", "a", "little", "lamb"))
)).toDF("id", "raw")
remover.transform(dataSet).show()
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.StopWordsRemover;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
StopWordsRemover remover = new StopWordsRemover()
.setInputCol("raw")
.setOutputCol("filtered");
List<Row> data = Arrays.asList(
RowFactory.create(Arrays.asList("I", "saw", "the", "red", "baloon")),
RowFactory.create(Arrays.asList("Mary", "had", "a", "little", "lamb"))
);
StructType schema = new StructType(new StructField[]{
new StructField(
"raw", DataTypes.createArrayType(DataTypes.StringType), false, Metadata.empty())
});
Dataset<Row> dataset = spark.createDataFrame(data, schema);
remover.transform(dataset).show();
Python:
from pyspark.ml.feature import StopWordsRemover
sentenceData = spark.createDataFrame([
(0, ["I", "saw", "the", "red", "baloon"]),
(1, ["Mary", "had", "a", "little", "lamb"])
], ["label", "raw"])
remover = StopWordsRemover(inputCol="raw", outputCol="filtered")
remover.transform(sentenceData).show(truncate=False)
n-gram
算法介紹:
一個n-gram是一個長度為整數n的字序列。NGram可以用來将輸入轉換為n-gram。
NGram的輸入為一系列字元串(如分詞器輸出)。參數n決定每個n-gram包含的對象個數。結果包含一系列n-gram,其中每個n-gram代表一個空格分割的n個連續字元。如果輸入少于n個字元串,将沒有輸出結果。
示例調用:
Scala:
import org.apache.spark.ml.feature.NGram
val wordDataFrame = spark.createDataFrame(Seq(
(0, Array("Hi", "I", "heard", "about", "Spark")),
(1, Array("I", "wish", "Java", "could", "use", "case", "classes")),
(2, Array("Logistic", "regression", "models", "are", "neat"))
)).toDF("label", "words")
val ngram = new NGram().setInputCol("words").setOutputCol("ngrams")
val ngramDataFrame = ngram.transform(wordDataFrame)
ngramDataFrame.take(3).map(_.getAs[Stream[String]]("ngrams").toList).foreach(println)
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.NGram;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
List<Row> data = Arrays.asList(
RowFactory.create(0.0, Arrays.asList("Hi", "I", "heard", "about", "Spark")),
RowFactory.create(1.0, Arrays.asList("I", "wish", "Java", "could", "use", "case", "classes")),
RowFactory.create(2.0, Arrays.asList("Logistic", "regression", "models", "are", "neat"))
);
StructType schema = new StructType(new StructField[]{
new StructField("label", DataTypes.DoubleType, false, Metadata.empty()),
new StructField(
"words", DataTypes.createArrayType(DataTypes.StringType), false, Metadata.empty())
});
Dataset<Row> wordDataFrame = spark.createDataFrame(data, schema);
NGram ngramTransformer = new NGram().setInputCol("words").setOutputCol("ngrams");
Dataset<Row> ngramDataFrame = ngramTransformer.transform(wordDataFrame);
for (Row r : ngramDataFrame.select("ngrams", "label").takeAsList(3)) {
java.util.List<String> ngrams = r.getList(0);
for (String ngram : ngrams) System.out.print(ngram + " --- ");
System.out.println();
}
Python:
from pyspark.ml.feature import NGram
wordDataFrame = spark.createDataFrame([
(0, ["Hi", "I", "heard", "about", "Spark"]),
(1, ["I", "wish", "Java", "could", "use", "case", "classes"]),
(2, ["Logistic", "regression", "models", "are", "neat"])
], ["label", "words"])
ngram = NGram(inputCol="words", outputCol="ngrams")
ngramDataFrame = ngram.transform(wordDataFrame)
for ngrams_label in ngramDataFrame.select("ngrams", "label").take(3):
print(ngrams_label)
Binarizer
算法介紹:
二值化是根據閥值将連續數值特征轉換為0-1特征的過程。
Binarizer參數有輸入、輸出以及閥值。特征值大于閥值将映射為1.0,特征值小于等于閥值将映射為0.0。
示例調用:
Scala:
import org.apache.spark.ml.feature.Binarizer
val data = Array((0, 0.1), (1, 0.8), (2, 0.2))
val dataFrame = spark.createDataFrame(data).toDF("label", "feature")
val binarizer: Binarizer = new Binarizer()
.setInputCol("feature")
.setOutputCol("binarized_feature")
.setThreshold(0.5)
val binarizedDataFrame = binarizer.transform(dataFrame)
val binarizedFeatures = binarizedDataFrame.select("binarized_feature")
binarizedFeatures.collect().foreach(println)
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.Binarizer;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
List<Row> data = Arrays.asList(
RowFactory.create(0, 0.1),
RowFactory.create(1, 0.8),
RowFactory.create(2, 0.2)
);
StructType schema = new StructType(new StructField[]{
new StructField("id", DataTypes.IntegerType, false, Metadata.empty()),
new StructField("feature", DataTypes.DoubleType, false, Metadata.empty())
});
Dataset<Row> continuousDataFrame = spark.createDataFrame(data, schema);
Binarizer binarizer = new Binarizer()
.setInputCol("feature")
.setOutputCol("binarized_feature")
.setThreshold(0.5);
Dataset<Row> binarizedDataFrame = binarizer.transform(continuousDataFrame);
Dataset<Row> binarizedFeatures = binarizedDataFrame.select("binarized_feature");
for (Row r : binarizedFeatures.collectAsList()) {
Double binarized_value = r.getDouble(0);
System.out.println(binarized_value);
}
Python:
from pyspark.ml.feature import Binarizer
continuousDataFrame = spark.createDataFrame([
(0, 0.1),
(1, 0.8),
(2, 0.2)
], ["label", "feature"])
binarizer = Binarizer(threshold=0.5, inputCol="feature", outputCol="binarized_feature")
binarizedDataFrame = binarizer.transform(continuousDataFrame)
binarizedFeatures = binarizedDataFrame.select("binarized_feature")
for binarized_feature, in binarizedFeatures.collect():
print(binarized_feature)
PCA
算法介紹:
主成分分析是一種統計學方法,它使用正交轉換從一系列可能相關的變量中提取線性無關變量集,提取出的變量集中的元素稱為主成分。使用PCA方法可以對變量集合進行降維。下面的示例将會展示如何将5維特征向量轉換為3維主成分向量。
示例調用:
Scala:
import org.apache.spark.ml.feature.PCA
import org.apache.spark.ml.linalg.Vectors
val data = Array(
Vectors.sparse(5, Seq((1, 1.0), (3, 7.0))),
Vectors.dense(2.0, 0.0, 3.0, 4.0, 5.0),
Vectors.dense(4.0, 0.0, 0.0, 6.0, 7.0)
)
val df = spark.createDataFrame(data.map(Tuple1.apply)).toDF("features")
val pca = new PCA()
.setInputCol("features")
.setOutputCol("pcaFeatures")
.setK(3)
.fit(df)
val pcaDF = pca.transform(df)
val result = pcaDF.select("pcaFeatures")
result.show()
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.PCA;
import org.apache.spark.ml.feature.PCAModel;
import org.apache.spark.ml.linalg.VectorUDT;
import org.apache.spark.ml.linalg.Vectors;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
List<Row> data = Arrays.asList(
RowFactory.create(Vectors.sparse(5, new int[]{1, 3}, new double[]{1.0, 7.0})),
RowFactory.create(Vectors.dense(2.0, 0.0, 3.0, 4.0, 5.0)),
RowFactory.create(Vectors.dense(4.0, 0.0, 0.0, 6.0, 7.0))
);
StructType schema = new StructType(new StructField[]{
new StructField("features", new VectorUDT(), false, Metadata.empty()),
});
Dataset<Row> df = spark.createDataFrame(data, schema);
PCAModel pca = new PCA()
.setInputCol("features")
.setOutputCol("pcaFeatures")
.setK(3)
.fit(df);
Dataset<Row> result = pca.transform(df).select("pcaFeatures");
result.show();
Python:
from pyspark.ml.feature import PCA
from pyspark.ml.linalg import Vectors
data = [(Vectors.sparse(5, [(1, 1.0), (3, 7.0)]),),
(Vectors.dense([2.0, 0.0, 3.0, 4.0, 5.0]),),
(Vectors.dense([4.0, 0.0, 0.0, 6.0, 7.0]),)]
df = spark.createDataFrame(data, ["features"])
pca = PCA(k=3, inputCol="features", outputCol="pcaFeatures")
model = pca.fit(df)
result = model.transform(df).select("pcaFeatures")
result.show(truncate=False)
PolynomialExpansion
算法介紹:
多項式擴充通過産生n維組合将原始特征将特征擴充到多項式空間。下面的示例會介紹如何将你的特征集拓展到3維多項式空間。
示例調用:
Scala:
import org.apache.spark.ml.feature.PolynomialExpansion
import org.apache.spark.ml.linalg.Vectors
val data = Array(
Vectors.dense(-2.0, 2.3),
Vectors.dense(0.0, 0.0),
Vectors.dense(0.6, -1.1)
)
val df = spark.createDataFrame(data.map(Tuple1.apply)).toDF("features")
val polynomialExpansion = new PolynomialExpansion()
.setInputCol("features")
.setOutputCol("polyFeatures")
.setDegree(3)
val polyDF = polynomialExpansion.transform(df)
polyDF.select("polyFeatures").take(3).foreach(println)
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.PolynomialExpansion;
import org.apache.spark.ml.linalg.VectorUDT;
import org.apache.spark.ml.linalg.Vectors;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
PolynomialExpansion polyExpansion = new PolynomialExpansion()
.setInputCol("features")
.setOutputCol("polyFeatures")
.setDegree(3);
List<Row> data = Arrays.asList(
RowFactory.create(Vectors.dense(-2.0, 2.3)),
RowFactory.create(Vectors.dense(0.0, 0.0)),
RowFactory.create(Vectors.dense(0.6, -1.1))
);
StructType schema = new StructType(new StructField[]{
new StructField("features", new VectorUDT(), false, Metadata.empty()),
});
Dataset<Row> df = spark.createDataFrame(data, schema);
Dataset<Row> polyDF = polyExpansion.transform(df);
List<Row> rows = polyDF.select("polyFeatures").takeAsList(3);
for (Row r : rows) {
System.out.println(r.get(0));
}
Python:
from pyspark.ml.feature import PolynomialExpansion
from pyspark.ml.linalg import Vectors
df = spark\
.createDataFrame([(Vectors.dense([-2.0, 2.3]),),
(Vectors.dense([0.0, 0.0]),),
(Vectors.dense([0.6, -1.1]),)],
["features"])
px = PolynomialExpansion(degree=3, inputCol="features", outputCol="polyFeatures")
polyDF = px.transform(df)
for expanded in polyDF.select("polyFeatures").take(3):
print(expanded)
Discrete Cosine Transform(DCT)
算法介紹:
離散餘弦變換是與傅裡葉變換相關的一種變換,它類似于離散傅立葉變換但是隻使用實數。離散餘弦變換相當于一個長度大概是它兩倍的離散傅裡葉變換,這個離散傅裡葉變換是對一個實偶函數進行的(因為一個實偶函數的傅裡葉變換仍然是一個實偶函數)。離散餘弦變換,經常被信号處理和圖像處理使用,用于對信号和圖像(包括靜止圖像和運動圖像)進行有損資料壓縮。
示例調用:
Scala:
import org.apache.spark.ml.feature.DCT
import org.apache.spark.ml.linalg.Vectors
val data = Seq(
Vectors.dense(0.0, 1.0, -2.0, 3.0),
Vectors.dense(-1.0, 2.0, 4.0, -7.0),
Vectors.dense(14.0, -2.0, -5.0, 1.0))
val df = spark.createDataFrame(data.map(Tuple1.apply)).toDF("features")
val dct = new DCT()
.setInputCol("features")
.setOutputCol("featuresDCT")
.setInverse(false)
val dctDf = dct.transform(df)
dctDf.select("featuresDCT").show(3)
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.DCT;
import org.apache.spark.ml.linalg.VectorUDT;
import org.apache.spark.ml.linalg.Vectors;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
List<Row> data = Arrays.asList(
RowFactory.create(Vectors.dense(0.0, 1.0, -2.0, 3.0)),
RowFactory.create(Vectors.dense(-1.0, 2.0, 4.0, -7.0)),
RowFactory.create(Vectors.dense(14.0, -2.0, -5.0, 1.0))
);
StructType schema = new StructType(new StructField[]{
new StructField("features", new VectorUDT(), false, Metadata.empty()),
});
Dataset<Row> df = spark.createDataFrame(data, schema);
DCT dct = new DCT()
.setInputCol("features")
.setOutputCol("featuresDCT")
.setInverse(false);
Dataset<Row> dctDf = dct.transform(df);
dctDf.select("featuresDCT").show(3);
Python:
from pyspark.ml.feature import DCT
from pyspark.ml.linalg import Vectors
df = spark.createDataFrame([
(Vectors.dense([0.0, 1.0, -2.0, 3.0]),),
(Vectors.dense([-1.0, 2.0, 4.0, -7.0]),),
(Vectors.dense([14.0, -2.0, -5.0, 1.0]),)], ["features"])
dct = DCT(inverse=False, inputCol="features", outputCol="featuresDCT")
dctDf = dct.transform(df)
for dcts in dctDf.select("featuresDCT").take(3):
print(dcts)
STringindexer
算法介紹:
StringIndexer将字元串标簽編碼為标簽名額。名額取值範圍為[0,numLabels],按照标簽出現頻率排序,是以出現最頻繁的标簽其名額為0。如果輸入列為數值型,我們先将之映射到字元串然後再對字元串的值進行名額。如果下遊的管道節點需要使用字元串-名額标簽,則必須将輸入和鑽還為字元串-名額列名。
示例:
假設我們有DataFrame資料含有id和category兩列:
id | category
----|----------
0 | a
1 | b
2 | c
3 | a
4 | a
5 | c
category是有3種取值的字元串列,使用StringIndexer進行轉換後我們可以得到如下輸出:
id | category |categoryIndex
----|----------|---------------
0 |a | 0.0
1 |b | 2.0
2 |c | 1.0
3 |a | 0.0
4 |a | 0.0
5 |c | 1.0
另外,如果在轉換新資料時出現了在訓練中未出現的标簽,StringIndexer将會報錯(預設值)或者跳過未出現的标簽執行個體。
示例調用:
Scala:
import org.apache.spark.ml.feature.StringIndexer
val df = spark.createDataFrame(
Seq((0, "a"), (1, "b"), (2, "c"), (3, "a"), (4, "a"), (5, "c"))
).toDF("id", "category")
val indexer = new StringIndexer()
.setInputCol("category")
.setOutputCol("categoryIndex")
val indexed = indexer.fit(df).transform(df)
indexed.show()
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.StringIndexer;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
import static org.apache.spark.sql.types.DataTypes.*;
List<Row> data = Arrays.asList(
RowFactory.create(0, "a"),
RowFactory.create(1, "b"),
RowFactory.create(2, "c"),
RowFactory.create(3, "a"),
RowFactory.create(4, "a"),
RowFactory.create(5, "c")
);
StructType schema = new StructType(new StructField[]{
createStructField("id", IntegerType, false),
createStructField("category", StringType, false)
});
Dataset<Row> df = spark.createDataFrame(data, schema);
StringIndexer indexer = new StringIndexer()
.setInputCol("category")
.setOutputCol("categoryIndex");
Dataset<Row> indexed = indexer.fit(df).transform(df);
indexed.show();
Python:
from pyspark.ml.feature import StringIndexer
df = spark.createDataFrame(
[(0, "a"), (1, "b"), (2, "c"), (3, "a"), (4, "a"), (5, "c")],
["id", "category"])
indexer = StringIndexer(inputCol="category", outputCol="categoryIndex")
indexed = indexer.fit(df).transform(df)
indexed.show()
IndexToString
算法介紹:
與StringIndexer對應,IndexToString将名額标簽映射回原始字元串标簽。一個常用的場景是先通過StringIndexer産生名額标簽,然後使用名額标簽進行訓練,最後再對預測結果使用IndexToString來擷取其原始的标簽字元串。
示例:
假設我們有如下的DataFrame包含id和categoryIndex兩列:
id | categoryIndex
----|---------------
0 | 0.0
1 | 2.0
2 | 1.0
3 | 0.0
4 | 0.0
5 | 1.0
使用originalCategory我們可以擷取其原始的标簽字元串如下:
id | categoryIndex| originalCategory
----|---------------|-----------------
0 |0.0 | a
1 |2.0 | b
2 |1.0 | c
3 |0.0 | a
4 |0.0 | a
5 |1.0 | c
示例調用:
Scala:
import org.apache.spark.ml.feature.{IndexToString, StringIndexer}
val df = spark.createDataFrame(Seq(
(0, "a"),
(1, "b"),
(2, "c"),
(3, "a"),
(4, "a"),
(5, "c")
)).toDF("id", "category")
val indexer = new StringIndexer()
.setInputCol("category")
.setOutputCol("categoryIndex")
.fit(df)
val indexed = indexer.transform(df)
val converter = new IndexToString()
.setInputCol("categoryIndex")
.setOutputCol("originalCategory")
val converted = converter.transform(indexed)
converted.select("id", "originalCategory").show()
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.IndexToString;
import org.apache.spark.ml.feature.StringIndexer;
import org.apache.spark.ml.feature.StringIndexerModel;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
List<Row> data = Arrays.asList(
RowFactory.create(0, "a"),
RowFactory.create(1, "b"),
RowFactory.create(2, "c"),
RowFactory.create(3, "a"),
RowFactory.create(4, "a"),
RowFactory.create(5, "c")
);
StructType schema = new StructType(new StructField[]{
new StructField("id", DataTypes.IntegerType, false, Metadata.empty()),
new StructField("category", DataTypes.StringType, false, Metadata.empty())
});
Dataset<Row> df = spark.createDataFrame(data, schema);
StringIndexerModel indexer = new StringIndexer()
.setInputCol("category")
.setOutputCol("categoryIndex")
.fit(df);
Dataset<Row> indexed = indexer.transform(df);
IndexToString converter = new IndexToString()
.setInputCol("categoryIndex")
.setOutputCol("originalCategory");
Dataset<Row> converted = converter.transform(indexed);
converted.select("id", "originalCategory").show();
Python:
from pyspark.ml.feature import IndexToString, StringIndexer
df = spark.createDataFrame(
[(0, "a"), (1, "b"), (2, "c"), (3, "a"), (4, "a"), (5, "c")],
["id", "category"])
stringIndexer = StringIndexer(inputCol="category", outputCol="categoryIndex")
model = stringIndexer.fit(df)
indexed = model.transform(df)
converter = IndexToString(inputCol="categoryIndex", outputCol="originalCategory")
converted = converter.transform(indexed)
converted.select("id", "originalCategory").show()
OneHotEncoder
算法介紹:
獨熱編碼将标簽名額映射為二值向量,其中最多一個單值。這種編碼被用于将種類特征使用到需要連續特征的算法,如邏輯回歸等。
示例調用:
Scala:
import org.apache.spark.ml.feature.{OneHotEncoder, StringIndexer}
val df = spark.createDataFrame(Seq(
(0, "a"),
(1, "b"),
(2, "c"),
(3, "a"),
(4, "a"),
(5, "c")
)).toDF("id", "category")
val indexer = new StringIndexer()
.setInputCol("category")
.setOutputCol("categoryIndex")
.fit(df)
val indexed = indexer.transform(df)
val encoder = new OneHotEncoder()
.setInputCol("categoryIndex")
.setOutputCol("categoryVec")
val encoded = encoder.transform(indexed)
encoded.select("id", "categoryVec").show()
Java:
import java.util.Arrays;
import java.util.List;
import org.apache.spark.ml.feature.OneHotEncoder;
import org.apache.spark.ml.feature.StringIndexer;
import org.apache.spark.ml.feature.StringIndexerModel;
import org.apache.spark.sql.Dataset;
import org.apache.spark.sql.Row;
import org.apache.spark.sql.RowFactory;
import org.apache.spark.sql.types.DataTypes;
import org.apache.spark.sql.types.Metadata;
import org.apache.spark.sql.types.StructField;
import org.apache.spark.sql.types.StructType;
List<Row> data = Arrays.asList(
RowFactory.create(0, "a"),
RowFactory.create(1, "b"),
RowFactory.create(2, "c"),
RowFactory.create(3, "a"),
RowFactory.create(4, "a"),
RowFactory.create(5, "c")
);
StructType schema = new StructType(new StructField[]{
new StructField("id", DataTypes.IntegerType, false, Metadata.empty()),
new StructField("category", DataTypes.StringType, false, Metadata.empty())
});
Dataset<Row> df = spark.createDataFrame(data, schema);
StringIndexerModel indexer = new StringIndexer()
.setInputCol("category")
.setOutputCol("categoryIndex")
.fit(df);
Dataset<Row> indexed = indexer.transform(df);
OneHotEncoder encoder = new OneHotEncoder()
.setInputCol("categoryIndex")
.setOutputCol("categoryVec");
Dataset<Row> encoded = encoder.transform(indexed);
encoded.select("id", "categoryVec").show();
Python:
from pyspark.ml.feature import OneHotEncoder, StringIndexer
df = spark.createDataFrame([
(0, "a"),
(1, "b"),
(2, "c"),
(3, "a"),
(4, "a"),
(5, "c")
], ["id", "category"])
stringIndexer = StringIndexer(inputCol="category", outputCol="categoryIndex")
model = stringIndexer.fit(df)
indexed = model.transform(df)
encoder = OneHotEncoder(dropLast=False, inputCol="categoryIndex", outputCol="categoryVec")
encoded = encoder.transform(indexed)
encoded.select("id", "categoryVec").show()