Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/5858#discussion_r29544396
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/DataFrameStatFunctions.scala ---
@@ -28,6 +28,32 @@ import org.apache.spark.sql.execution.stat._
final class DataFrameStatFunctions private[sql](df: DataFrame) {
/**
+ * Calculate the correlation of two columns of a DataFrame. Currently
only supports the Pearson
+ * Correlation Coefficient. For Spearman Correlation, consider using RDD
methods found in
+ * MLlib's Statistics.
+ *
+ * @param col1 the name of the column
+ * @param col2 the name of the column to calculate the correlation
against
+ * @return The Pearson Correlation Coefficient as a Double.
+ */
+ def corr(col1: String, col2: String, method: String): Double = {
+ assert(method == "pearson", "Currently only the calculation of the
Pearson Correlation " +
+ "coefficient is supported.")
+ StatFunctions.pearsonCorrelation(df, Seq(col1, col2))
+ }
+
+ /**
+ * Java Friendly implementation to calculate the Pearson correlation
coefficient of two columns.
--- End diff --
what's not java friendly?
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