The entry point into SparkR is the `SparkSession` which connects your R program to a Spark cluster.
You can create a `SparkSession` using `sparkR.session` and pass in options such as the application name, any spark packages depended on, etc. Further, you can also work with SparkDataFrames via `SparkSession`. If you are working from the `sparkR` shell, the `SparkSession` should already be created for you, and you would not need to call `sparkR.session`.
With a `SparkSession`, applications can create `SparkDataFrame`s from a local R data frame, from a [Hive table](sql-programming-guide.html#hive-tables), or from other [data sources](sql-programming-guide.html#data-sources).
The simplest way to create a data frame is to convert a local R data frame into a SparkDataFrame. Specifically we can use `as.DataFrame` or `createDataFrame` and pass in the local R data frame to create a SparkDataFrame. As an example, the following creates a `SparkDataFrame` based using the `faithful` dataset from R.
SparkR supports operating on a variety of data sources through the `SparkDataFrame` interface. This section describes the general methods for loading and saving data using Data Sources. You can check the Spark SQL programming guide for more [specific options](sql-programming-guide.html#manually-specifying-options) that are available for the built-in data sources.
The general method for creating SparkDataFrames from data sources is `read.df`. This method takes in the path for the file to load and the type of data source, and the currently active SparkSession will be used automatically.
SparkR supports reading JSON, CSV and Parquet files natively, and through packages available from sources like [Third Party Projects](https://cwiki.apache.org/confluence/display/SPARK/Third+Party+Projects), you can find data source connectors for popular file formats like Avro. These packages can either be added by
specifying `--packages` with `spark-submit` or `sparkR` commands, or if initializing SparkSession with `sparkPackages` parameter when in an interactive R shell or from RStudio.
We can see how to use data sources using an example JSON input file. Note that the file that is used here is _not_ a typical JSON file. Each line in the file must contain a separate, self-contained valid JSON object. As a consequence, a regular multi-line JSON file will most often fail.
# Similarly, multiple files can be read with read.json
people <-read.json(c("./examples/src/main/resources/people.json","./examples/src/main/resources/people2.json"))
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The data sources API natively supports CSV formatted input files. For more information please refer to SparkR [read.df](api/R/read.df.html) API documentation.
The data sources API can also be used to save out SparkDataFrames into multiple file formats. For example we can save the SparkDataFrame from the previous example
You can also create SparkDataFrames from Hive tables. To do this we will need to create a SparkSession with Hive support which can access tables in the Hive MetaStore. Note that Spark should have been built with [Hive support](building-spark.html#building-with-hive-and-jdbc-support) and more details can be found in the [SQL programming guide](sql-programming-guide.html#starting-point-sparksession). In SparkR, by default it will attempt to create a SparkSession with Hive support enabled (`enableHiveSupport = TRUE`).
SparkR data frames support a number of commonly used functions to aggregate data after grouping. For example we can compute a histogram of the `waiting` time in the `faithful` dataset as shown below
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{% highlight r %}
# We use the `n` operator to count the number of times each waiting time appears
SparkR also provides a number of functions that can directly applied to columns for data processing and during aggregation. The example below shows the use of basic arithmetic functions.
and should have only one parameter, to which a `data.frame` corresponds to each partition will be passed. The output of function should be a `data.frame`. Schema specifies the row format of the resulting a `SparkDataFrame`. It must match to [data types](#data-type-mapping-between-r-and-spark) of returned value.
should be a `data.frame`. But, Schema is not required to be passed. Note that `dapplyCollect` can fail if the output of UDF run on all the partition cannot be pulled to the driver and fit in driver memory.
#### Run a given function on a large dataset grouping by input column(s) and using `gapply` or `gapplyCollect`
##### gapply
Apply a function to each group of a `SparkDataFrame`. The function is to be applied to each group of the `SparkDataFrame` and should have only two parameters: grouping key and R `data.frame` corresponding to
that key. The groups are chosen from `SparkDataFrame`s column(s).
The output of function should be a `data.frame`. Schema specifies the row format of the resulting
`SparkDataFrame`. It must represent R function's output schema on the basis of Spark [data types](#data-type-mapping-between-r-and-spark). The column names of the returned `data.frame` are set by user.
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{% highlight r %}
# Determine six waiting times with the largest eruption time in minutes.
Like `gapply`, applies a function to each partition of a `SparkDataFrame` and collect the result back to R data.frame. The output of the function should be a `data.frame`. But, the schema is not required to be passed. Note that `gapplyCollect` can fail if the output of UDF run on all the partition cannot be pulled to the driver and fit in driver memory.
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{% highlight r %}
# Determine six waiting times with the largest eruption time in minutes.
SparkR supports the following machine learning algorithms currently: `Generalized Linear Model`, `Accelerated Failure Time (AFT) Survival Regression Model`, `Naive Bayes Model` and `KMeans Model`.
Under the hood, SparkR uses MLlib to train the model.
Users can call `summary` to print a summary of the fitted model, [predict](api/R/predict.html) to make predictions on new data, and [write.ml](api/R/write.ml.html)/[read.ml](api/R/read.ml.html) to save/load fitted models.
SparkR supports a subset of the available R formula operators for model fitting, including ‘~’, ‘.’, ‘:’, ‘+’, and ‘-‘.
When loading and attaching a new package in R, it is possible to have a name [conflict](https://stat.ethz.ch/R-manual/R-devel/library/base/html/library.html), where a
function is masking another function.
The following functions are masked by the SparkR package:
<tableclass="table">
<tr><th>Masked function</th><th>How to Access</th></tr>
<tr>
<td><code>cov</code> in <code>package:stats</code></td>
<td><code><pre>stats::cov(x, y = NULL, use = "everything",
Since part of SparkR is modeled on the `dplyr` package, certain functions in SparkR share the same names with those in `dplyr`. Depending on the load order of the two packages, some functions from the package loaded first are masked by those in the package loaded after. In such case, prefix such calls with the package name, for instance, `SparkR::cume_dist(x)` or `dplyr::cume_dist(x)`.
- Spark's `SQLContext` and `HiveContext` have been deprecated to be replaced by `SparkSession`. Instead of `sparkR.init()`, call `sparkR.session()` in its place to instantiate the SparkSession. Once that is done, that currently active SparkSession will be used for SparkDataFrame operations.
- The parameter `sparkExecutorEnv` is not supported by `sparkR.session`. To set environment for the executors, set Spark config properties with the prefix "spark.executorEnv.VAR_NAME", for example, "spark.executorEnv.PATH"
- The `sqlContext` parameter is no longer required for these functions: `createDataFrame`, `as.DataFrame`, `read.json`, `jsonFile`, `read.parquet`, `parquetFile`, `read.text`, `sql`, `tables`, `tableNames`, `cacheTable`, `uncacheTable`, `clearCache`, `dropTempTable`, `read.df`, `loadDF`, `createExternalTable`.
- The method `registerTempTable` has been deprecated to be replaced by `createOrReplaceTempView`.
- The method `dropTempTable` has been deprecated to be replaced by `dropTempView`.