Github user MLnick commented on a diff in the pull request:
https://github.com/apache/spark/pull/12574#discussion_r60825440
--- Diff: mllib/src/main/scala/org/apache/spark/ml/recommendation/ALS.scala
---
@@ -218,11 +292,135 @@ class ALSModel private[ml] (
predict(userFactors("features"),
itemFactors("features")).as($(predictionCol)))
}
+ /**
+ * Generate top `num` recommended items for each user (or recommended
users for each item) in the
+ * input [[DataFrame]].
+ * If `dstCol` exists in the input schema, then the result will contain
the recommendations and
+ * the actual "ground truth" ids (taken from those ids present in
`dstCol`). If `dstCol` doesn't
+ * exist, then the result will only contain recommendations.
+ * @param dataset [[DataFrame]] containing a column of user or item ids
for which to recommend.
+ * @param srcFactors user / item factors for which to generate top-k
recommendations.
+ * @param dstFactors candidate user / item factors from which to
generate top-k recommendations.
+ * @param srcCol name of column containing ids for which to recommend.
+ * @param dstCol name of column containing ids used to generate the
"ground truth" set (if the
+ * column exists).
+ * @param num how many recommended items (or users) to compute for each
user (or item)
+ * @return [[DataFrame]] containing recommendations (and "ground truth"
set if `dstCol` exists)
+ * for each id in `srcCol`.
+ */
+ private def recommendUsersOrItems(
+ dataset: Dataset[_],
+ srcFactors: DataFrame,
+ dstFactors: DataFrame,
+ srcCol: String,
+ dstCol: String,
+ num: Int): DataFrame = {
+
+ import dataset.sqlContext.implicits._
+ val schema = dataset.schema
+
+ val factors = dataset
+ .select(srcCol)
+ .distinct
+ .join(srcFactors, dataset(srcCol) === srcFactors("id"), "left")
+ .select(srcFactors("id"), srcFactors("features"))
+
+ val topKRaw = ALSModel.recommendForAll(rank, factors, dstFactors, num)
+ val topK = if ($(withScores)) {
+ // with scores, 'predictions' is an Array((id1, score1), (id2,
score2), ...)
+ topKRaw.toDF("id", "recommendations")
+ } else {
+ // without scores, 'predictions' is an Array(id1, id2, ...)
+ topKRaw
+ .map { case (id, predsWithScores) => (id,
predsWithScores.map(_._1)) }
+ .toDF("id", "recommendations")
+ }
+
+ val result = if (schema.fieldNames.contains(dstCol)) {
+ // if 'dstCol' exists, we group by that column to generate the
'ground truth' set of
+ // user (or item) ids.
+ // Note, this changes the structure of the input DataFrame,
returning a row of
+ // (id, predictions, actual) per unique id in 'srcCol', discarding
all other columns.
+ // In practice this is expected only during model selection with
+ // CrossValidator/TrainValidationSplit using RankingEvaluator.
+ val actual = dataset
+ .select(srcCol, dstCol)
+ .as[(Int, Int)]
+ .groupByKey(_._1)
+ .mapGroups { case (src, ids) => (src, ids.map(_._2).toArray) }
+ .toDF("id", "actual")
+
+ dataset
+ .select(srcCol)
+ .distinct
+ .join(topK, dataset(srcCol) === topK("id"))
+ .join(actual, dataset(srcCol) === actual("id"))
+ .select(
--- End diff --
I'll add a note to look into optimizing this when `cogroup` exists.
By the way, when you say that `dataset` is unlikely to contain many
duplicates, are you referring to duplicate rows? If so, yes that is true as
generally each `user, item, rating` tuple is distinct (though it's not
guaranteed to be the case).
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