coalesce: Coalesce

In SparkR: R Front End for 'Apache Spark'

Description

Returns a new SparkDataFrame that has exactly numPartitions partitions. This operation results in a narrow dependency, e.g. if you go from 1000 partitions to 100 partitions, there will not be a shuffle, instead each of the 100 new partitions will claim 10 of the current partitions. If a larger number of partitions is requested, it will stay at the current number of partitions.

Usage

coalesce(x, ...)

## S4 method for signature 'SparkDataFrame'
coalesce(x, numPartitions)

Arguments

x	a SparkDataFrame.
...	additional argument(s).
numPartitions	the number of partitions to use.

Details

However, if you're doing a drastic coalesce on a SparkDataFrame, e.g. to numPartitions = 1, this may result in your computation taking place on fewer nodes than you like (e.g. one node in the case of numPartitions = 1). To avoid this, call repartition. This will add a shuffle step, but means the current upstream partitions will be executed in parallel (per whatever the current partitioning is).

Note

coalesce(SparkDataFrame) since 2.1.1

See Also

repartition, repartitionByRange

Other SparkDataFrame functions: SparkDataFrame-class, agg(), alias(), arrange(), as.data.frame(), attach,SparkDataFrame-method, broadcast(), cache(), checkpoint(), collect(), colnames(), coltypes(), createOrReplaceTempView(), crossJoin(), cube(), dapplyCollect(), dapply(), describe(), dim(), distinct(), dropDuplicates(), dropna(), drop(), dtypes(), exceptAll(), except(), explain(), filter(), first(), gapplyCollect(), gapply(), getNumPartitions(), group_by(), head(), hint(), histogram(), insertInto(), intersectAll(), intersect(), isLocal(), isStreaming(), join(), limit(), localCheckpoint(), merge(), mutate(), ncol(), nrow(), persist(), printSchema(), randomSplit(), rbind(), rename(), repartitionByRange(), repartition(), rollup(), sample(), saveAsTable(), schema(), selectExpr(), select(), showDF(), show(), storageLevel(), str(), subset(), summary(), take(), toJSON(), unionAll(), unionByName(), union(), unpersist(), withColumn(), withWatermark(), with(), write.df(), write.jdbc(), write.json(), write.orc(), write.parquet(), write.stream(), write.text()

Examples

## Not run: 
sparkR.session()
path <- "path/to/file.json"
df <- read.json(path)
newDF <- coalesce(df, 1L)

## End(Not run)

SparkR documentation built on June 3, 2021, 5:05 p.m.