ngram: Machine Learning Feature Extractors

Άρθρο
02/28/2023

Feature Extractors that can be used with mtText.

Usage

  ngramCount(ngramLength = 1, skipLength = 0, maxNumTerms = 1e+07,
    weighting = "tf")

  ngramHash(ngramLength = 1, skipLength = 0, hashBits = 16,
    seed = 314489979, ordered = TRUE, invertHash = 0)

Arguments

`ngramLength`

An integer that specifies the maximum number of tokens to take when constructing an n-gram. The default value is 1.

`skipLength`

An integer that specifies the maximum number of tokens to skip when constructing an n-gram. If the value specified as skip length is k, then n-grams can contain up to k skips (not necessarily consecutive). For example, if k=2, then the 3-grams extracted from the text "the sky is blue today" are: "the sky is", "the sky blue", "the sky today", "the is blue", "the is today" and "the blue today". The default value is 0.

`maxNumTerms`

An integer that specifies the maximum number of categories to include in the dictionary. The default value is 10000000.

`weighting`

A character string that specifies the weighting criteria:

"tf": to use term frequency.
"idf": to use inverse document frequency.
"tfidf": to use both term frequency and inverse document frequency.

`hashBits`

integer value. Number of bits to hash into. Must be between 1 and 30, inclusive.

`seed`

integer value. Hashing seed.

`ordered`

TRUE to include the position of each term in the hash. Otherwise, FALSE. The default value is TRUE.

`invertHash`

An integer specifying the limit on the number of keys that can be used to generate the slot name. 0 means no invert hashing; -1 means no limit. While a zero value gives better performance, a non-zero value is needed to get meaningful coefficient names.

Details

ngramCount allows defining arguments for count-based feature extraction. It accepts following options: ngramLength, skipLength, maxNumTerms and weighting.

ngramHash allows defining arguments for hashing-based feature extraction. It accepts the following options: ngramLength, skipLength, hashBits, seed, ordered and invertHash.

Value

A character string defining the transform.

Author(s)

Microsoft Corporation Microsoft Technical Support

Examples


  myData <- data.frame(opinion = c(
     "I love it!",
     "I love it!",
     "Love it!",
     "I love it a lot!",
     "Really love it!",
     "I hate it",
     "I hate it",
     "I hate it.",
     "Hate it",
     "Hate"),
     like = rep(c(TRUE, FALSE), each = 5),
     stringsAsFactors = FALSE)

 outModel1 <- rxLogisticRegression(like~opinionCount, data = myData, 
     mlTransforms = list(featurizeText(vars = c(opinionCount = "opinion"), 
         wordFeatureExtractor = ngramHash(invertHash = -1, hashBits = 3)))) 
 summary(outModel1)   

 outModel2 <- rxLogisticRegression(like~opinionCount, data = myData, 
     mlTransforms = list(featurizeText(vars = c(opinionCount = "opinion"), 
         wordFeatureExtractor = ngramCount(maxNumTerms = 5, weighting = "tf"))))         
 summary(outModel2)

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