Partition a Spark Dataframe
Partition a Spark DataFrame into multiple groups. This routine is useful for splitting a DataFrame into, for example, training and test datasets.
sdf_partition(x, ..., weights = NULL, seed = sample(.Machine$integer.max, 1))
- An object coercable to a Spark DataFrame.
- Named parameters, mapping table names to weights. The weights will be normalized such that they sum to 1.
- An alternate mechanism for supplying weights -- when
specified, this takes precedence over the
- Random seed to use for randomly partitioning the dataset. Set this if you want your partitioning to be reproducible on repeated runs.
The sampling weights define the probability that a particular observation will be assigned to a particular partition, not the resulting size of the partition. This implies that partitioning a DataFrame with, for example,
sdf_partition(x, training = 0.5, test = 0.5)
is not guaranteed to produce
of equal size.
Transforming Spark DataFrames
The family of functions prefixed with
sdf_ generally access the Scala
Spark DataFrame API directly, as opposed to the
dplyr interface which
uses Spark SQL. These functions will 'force' any pending SQL in a
dplyr pipeline, such that the resulting
returned will no longer have the attached 'lazy' SQL operations. Note that
the underlying Spark DataFrame does execute its operations lazily, so
that even though the pending set of operations (currently) are not exposed at
the R level, these operations will only be executed when you explicitly
collect() the table.
## Not run: # # randomly partition data into a 'training' and 'test' # # dataset, with 60% of the observations assigned to the # # 'training' dataset, and 40% assigned to the 'test' dataset # data(diamonds, package = "ggplot2") # diamonds_tbl <- copy_to(sc, diamonds, "diamonds") # partitions <- diamonds_tbl %>% # sdf_partition(training = 0.6, test = 0.4) # print(partitions) # # # alternate way of specifying weights # weights <- c(training = 0.6, test = 0.4) # diamonds_tbl %>% sdf_partition(weights = weights) # ## End(Not run)