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https://issues.apache.org/jira/browse/SPARK-14657?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xiangrui Meng updated SPARK-14657:
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Assignee: Yanbo Liang
> RFormula output wrong features when formula w/o intercept
> ---------------------------------------------------------
>
> Key: SPARK-14657
> URL: https://issues.apache.org/jira/browse/SPARK-14657
> Project: Spark
> Issue Type: Bug
> Components: ML
> Reporter: Yanbo Liang
> Assignee: Yanbo Liang
>
> SparkR::glm output different features compared with R glm when fit w/o
> intercept and having string/category features. Take the following example,
> SparkR output three features compared with four features for native R.
> SparkR::glm
> {quote}
> training <- suppressWarnings(createDataFrame(sqlContext, iris))
> model <- glm(Sepal_Width ~ Sepal_Length + Species - 1, data = training)
> summary(model)
> Coefficients:
> Estimate Std. Error t value Pr(>|t|)
> Sepal_Length 0.67468 0.0093013 72.536 0
> Species_versicolor -1.2349 0.07269 -16.989 0
> Species_virginica -1.4708 0.077397 -19.003 0
> {quote}
> stats::glm
> {quote}
> summary(glm(Sepal.Width ~ Sepal.Length + Species - 1, data = iris))
> Coefficients:
> Estimate Std. Error t value Pr(>|t|)
> Sepal.Length 0.3499 0.0463 7.557 4.19e-12 ***
> Speciessetosa 1.6765 0.2354 7.123 4.46e-11 ***
> Speciesversicolor 0.6931 0.2779 2.494 0.0137 *
> Speciesvirginica 0.6690 0.3078 2.174 0.0313 *
> {quote}
> The encoder for string/category feature is different. R did not drop any
> category but SparkR drop the last one.
> I searched online and test some other cases, found when we fit R glm model(or
> other models powered by R formula) w/o intercept on a dataset including
> string/category features, one of the categories in the first category feature
> is being used as reference category, we will not drop any category for that
> feature.
> I think we should keep consistent semantics between Spark RFormula and R
> formula.
> cc [~mengxr]
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