Github user felixcheung commented on a diff in the pull request:
https://github.com/apache/spark/pull/16951#discussion_r101454138
--- Diff: R/pkg/R/stats.R ---
@@ -149,15 +149,18 @@ setMethod("freqItems", signature(x =
"SparkDataFrame", cols = "character"),
#' This method implements a variation of the Greenwald-Khanna algorithm
(with some speed
#' optimizations). The algorithm was first present in
[[http://dx.doi.org/10.1145/375663.375670
#' Space-efficient Online Computation of Quantile Summaries]] by Greenwald
and Khanna.
+#' Note that rows containing any NA values will be removed before
calculation.
#'
#' @param x A SparkDataFrame.
-#' @param col The name of the numerical column.
+#' @param cols The names of the numerical columns.
#' @param probabilities A list of quantile probabilities. Each number must
belong to [0, 1].
#' For example 0 is the minimum, 0.5 is the median, 1
is the maximum.
#' @param relativeError The relative target precision to achieve (>= 0).
If set to zero,
#' the exact quantiles are computed, which could be
very expensive.
#' Note that values greater than 1 are accepted but
give the same result as 1.
-#' @return The approximate quantiles at the given probabilities.
+#' @return The approximate quantiles at the given probabilities. The
output should be a list,
+#' and each element in it is a list of numeric values which
represents the approximate
+#' quantiles in corresponding column.
--- End diff --
this would break the output format - I'm not sure if we should do this
in-place, rather than a new signature/return value for multiple columns
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