sparklyr-R语言访问Spark的另外一种方法

Posted 2020-09-26 董俊杰

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篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了sparklyr-R语言访问Spark的另外一种方法相关的知识，希望对你有一定的参考价值。

Connect to Spark from R. The sparklyr package provides a
complete dplyr backend.
Filter and aggregate Spark datasets then bring them into R for
analysis and visualization.
Use Spark<u+2019>s distributed machine learning library from R.
Create extensions that call the full Spark API and provide
interfaces to Spark packages.

Installation

You can install the sparklyr package from CRAN as follows:

install.packages("sparklyr")

You should also install a local version of Spark for development purposes:

library(sparklyr)
spark_install(version = "1.6.2")

To upgrade to the latest version of sparklyr, run the following command and restart your r session:

devtools::install_github("rstudio/sparklyr")

If you use the RStudio IDE, you should also download the latest preview release of the IDE which includes several enhancements for interacting with Spark (see the RStudio IDE section below for more details).

Connecting to Spark

You can connect to both local instances of Spark as well as remote Spark clusters. Here we<u+2019>ll connect to a local instance of Spark via the spark_connect function:

library(sparklyr)
sc <- spark_connect(master = "local")

The returned Spark connection (sc) provides a remote dplyr data source to the Spark cluster.

For more information on connecting to remote Spark clusters see the Deployment section of the sparklyr website.

Using dplyr

We can new use all of the available dplyr verbs against the tables within the cluster.

We<u+2019>ll start by copying some datasets from R into the Spark cluster (note that you may need to install the nycflights13 and Lahman packages in order to execute this code):

install.packages(c("nycflights13", "Lahman"))

library(dplyr)
iris_tbl <- copy_to(sc, iris)
flights_tbl <- copy_to(sc, nycflights13::flights, "flights")
batting_tbl <- copy_to(sc, Lahman::Batting, "batting")
src_tbls(sc)

## [1] "batting" "flights" "iris"

To start with here<u+2019>s a simple filtering example:

# filter by departure delay and print the first few records
flights_tbl %>% filter(dep_delay == 2)

## Source:   query [6,233 x 19]
## Database: spark connection master=local[8] app=sparklyr local=TRUE
## 
##     year month   day dep_time sched_dep_time dep_delay arr_time
##    <int> <int> <int>    <int>          <int>     <dbl>    <int>
## 1   2013     1     1      517            515         2      830
## 2   2013     1     1      542            540         2      923
## 3   2013     1     1      702            700         2     1058
## 4   2013     1     1      715            713         2      911
## 5   2013     1     1      752            750         2     1025
## 6   2013     1     1      917            915         2     1206
## 7   2013     1     1      932            930         2     1219
## 8   2013     1     1     1028           1026         2     1350
## 9   2013     1     1     1042           1040         2     1325
## 10  2013     1     1     1231           1229         2     1523
## # ... with 6,223 more rows, and 12 more variables: sched_arr_time <int>,
## #   arr_delay <dbl>, carrier <chr>, flight <int>, tailnum <chr>,
## #   origin <chr>, dest <chr>, air_time <dbl>, distance <dbl>, hour <dbl>,
## #   minute <dbl>, time_hour <dbl>

Introduction to dplyr provides additional dplyr examples you can try. For example, consider the last example from the tutorial which plots data on flight delays:

delay <- flights_tbl %>% 
  group_by(tailnum) %>%
  summarise(count = n(), dist = mean(distance), delay = mean(arr_delay)) %>%
  filter(count > 20, dist < 2000, !is.na(delay)) %>%
  collect

# plot delays
library(ggplot2)
ggplot(delay, aes(dist, delay)) +
  geom_point(aes(size = count), alpha = 1/2) +
  geom_smooth() +
  scale_size_area(max_size = 2)

## `geom_smooth()` using method = ‘gam‘

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Window Functions

dplyr window functions are also supported, for example:

batting_tbl %>%
  select(playerID, yearID, teamID, G, AB:H) %>%
  arrange(playerID, yearID, teamID) %>%
  group_by(playerID) %>%
  filter(min_rank(desc(H)) <= 2 & H > 0)

## Source:   query [2.562e+04 x 7]
## Database: spark connection master=local[8] app=sparklyr local=TRUE
## Groups: playerID
## 
##     playerID yearID teamID     G    AB     R     H
##        <chr>  <int>  <chr> <int> <int> <int> <int>
## 1  abbotpa01   2000    SEA    35     5     1     2
## 2  abbotpa01   2004    PHI    10    11     1     2
## 3  abnersh01   1992    CHA    97   208    21    58
## 4  abnersh01   1990    SDN    91   184    17    45
## 5  abreujo02   2015    CHA   154   613    88   178
## 6  abreujo02   2014    CHA   145   556    80   176
## 7  acevejo01   2001    CIN    18    34     1     4
## 8  acevejo01   2004    CIN    39    43     0     2
## 9  adamsbe01   1919    PHI    78   232    14    54
## 10 adamsbe01   1918    PHI    84   227    10    40
## # ... with 2.561e+04 more rows

For additional documentation on using dplyr with Spark see the dplyr section of the sparklyr website.

Using SQL

It<u+2019>s also possible to execute SQL queries directly against tables within a Spark cluster. The spark_connection object implements a DBI interface for Spark, so you can use dbGetQuery to execute SQL and return the result as an R data frame:

library(DBI)
iris_preview <- dbGetQuery(sc, "SELECT * FROM iris LIMIT 10")
iris_preview

##    Sepal_Length Sepal_Width Petal_Length Petal_Width Species
## 1           5.1         3.5          1.4         0.2  setosa
## 2           4.9         3.0          1.4         0.2  setosa
## 3           4.7         3.2          1.3         0.2  setosa
## 4           4.6         3.1          1.5         0.2  setosa
## 5           5.0         3.6          1.4         0.2  setosa
## 6           5.4         3.9          1.7         0.4  setosa
## 7           4.6         3.4          1.4         0.3  setosa
## 8           5.0         3.4          1.5         0.2  setosa
## 9           4.4         2.9          1.4         0.2  setosa
## 10          4.9         3.1          1.5         0.1  setosa

Machine Learning

You can orchestrate machine learning algorithms in a Spark cluster via the machine learning functions within sparklyr. These functions connect to a set of high-level APIs built on top of DataFrames that help you create and tune machine learning workflows.

Here<u+2019>s an example where we use ml_linear_regression to fit a linear regression model. We<u+2019>ll use the built-in mtcars dataset, and see if we can predict a car<u+2019>s fuel consumption (mpg) based on its weight (wt), and the number of cylinders the engine contains (cyl). We<u+2019>ll assume in each case that the relationship between mpg and each of our features is linear.

# copy mtcars into spark
mtcars_tbl <- copy_to(sc, mtcars)

# transform our data set, and then partition into ‘training‘, ‘test‘
partitions <- mtcars_tbl %>%
  filter(hp >= 100) %>%
  mutate(cyl8 = cyl == 8) %>%
  sdf_partition(training = 0.5, test = 0.5, seed = 1099)

# fit a linear model to the training dataset
fit <- partitions$training %>%
  ml_linear_regression(response = "mpg", features = c("wt", "cyl"))

## * No rows dropped by ‘na.omit‘ call

fit

## Call: ml_linear_regression(., response = "mpg", features = c("wt", "cyl"))
## 
## Coefficients:
## (Intercept)          wt         cyl 
##   37.066699   -2.309504   -1.639546

For linear regression models produced by Spark, we can use summary() to learn a bit more about the quality of our fit, and the statistical significance of each of our predictors.

summary(fit)

## Call: ml_linear_regression(., response = "mpg", features = c("wt", "cyl"))
## 
## Deviance Residuals::
##     Min      1Q  Median      3Q     Max 
## -2.6881 -1.0507 -0.4420  0.4757  3.3858 
## 
## Coefficients:
##             Estimate Std. Error t value  Pr(>|t|)    
## (Intercept) 37.06670    2.76494 13.4059 2.981e-07 ***
## wt          -2.30950    0.84748 -2.7252   0.02341 *  
## cyl         -1.63955    0.58635 -2.7962   0.02084 *  
## ---
## Signif. codes:  0 ‘***‘ 0.001 ‘**‘ 0.01 ‘*‘ 0.05 ‘.‘ 0.1 ‘ ‘ 1
## 
## R-Squared: 0.8665
## Root Mean Squared Error: 1.799

Spark machine learning supports a wide array of algorithms and feature transformations and as illustrated above it<u+2019>s easy to chain these functions together with dplyr pipelines. To learn more see the machine learning section.

Reading and Writing Data

You can read and write data in CSV, JSON, and Parquet formats. Data can be stored in HDFS, S3, or on the local filesystem of cluster nodes.

temp_csv <- tempfile(fileext = ".csv")
temp_parquet <- tempfile(fileext = ".parquet")
temp_json <- tempfile(fileext = ".json")

spark_write_csv(iris_tbl, temp_csv)
iris_csv_tbl <- spark_read_csv(sc, "iris_csv", temp_csv)

spark_write_parquet(iris_tbl, temp_parquet)
iris_parquet_tbl <- spark_read_parquet(sc, "iris_parquet", temp_parquet)

spark_write_json(iris_tbl, temp_json)
iris_json_tbl <- spark_read_json(sc, "iris_json", temp_json)

src_tbls(sc)

## [1] "batting"      "flights"      "iris"         "iris_csv"    
## [5] "iris_json"    "iris_parquet" "mtcars"

Extensions

The facilities used internally by sparklyr for its dplyr and machine learning interfaces are available to extension packages. Since Spark is a general purpose cluster computing system there are many potential applications for extensions (e.g.<u+00a0>interfaces to custom machine learning pipelines, interfaces to 3rd party Spark packages, etc.).

Here<u+2019>s a simple example that wraps a Spark text file line counting function with an R function:

# write a CSV 
tempfile <- tempfile(fileext = ".csv")
write.csv(nycflights13::flights, tempfile, row.names = FALSE, na = "")

# define an R interface to Spark line counting
count_lines <- function(sc, path) {
  spark_context(sc) %>% 
    invoke("textFile", path, 1L) %>% 
      invoke("count")
}

# call spark to count the lines of the CSV
count_lines(sc, tempfile)

## [1] 336777

To learn more about creating extensions see the Extensions section of the sparklyr website.

Table Utilities

You can cache a table into memory with:

tbl_cache(sc, "batting")

and unload from memory using:

tbl_uncache(sc, "batting")

Connection Utilities

You can view the Spark web console using the spark_web function:

spark_web(sc)

You can show the log using the spark_log function:

spark_log(sc, n = 10)

## 17/02/03 15:34:17 INFO DAGScheduler: Submitting 1 missing tasks from ResultStage 91 (/var/folders/fz/v6wfsg2x1fb1rw4f6r0x4jwm0000gn/T//RtmpZqMbDE/file8f2b280ac4e5.csv MapPartitionsRDD[363] at textFile at NativeMethodAccessorImpl.java:-2)
## 17/02/03 15:34:17 INFO TaskSchedulerImpl: Adding task set 91.0 with 1 tasks
## 17/02/03 15:34:17 INFO TaskSetManager: Starting task 0.0 in stage 91.0 (TID 177, localhost, partition 0,PROCESS_LOCAL, 2430 bytes)
## 17/02/03 15:34:17 INFO Executor: Running task 0.0 in stage 91.0 (TID 177)
## 17/02/03 15:34:17 INFO HadoopRDD: Input split: file:/var/folders/fz/v6wfsg2x1fb1rw4f6r0x4jwm0000gn/T/RtmpZqMbDE/file8f2b280ac4e5.csv:0+33313106
## 17/02/03 15:34:17 INFO Executor: Finished task 0.0 in stage 91.0 (TID 177). 2082 bytes result sent to driver
## 17/02/03 15:34:17 INFO TaskSetManager: Finished task 0.0 in stage 91.0 (TID 177) in 116 ms on localhost (1/1)
## 17/02/03 15:34:17 INFO DAGScheduler: ResultStage 91 (count at NativeMethodAccessorImpl.java:-2) finished in 0.117 s
## 17/02/03 15:34:17 INFO TaskSchedulerImpl: Removed TaskSet 91.0, whose tasks have all completed, from pool 
## 17/02/03 15:34:17 INFO DAGScheduler: Job 61 finished: count at NativeMethodAccessorImpl.java:-2, took 0.119612 s

Finally, we disconnect from Spark:

spark_disconnect(sc)

RStudio IDE

The latest RStudio Preview Release of the RStudio IDE includes integrated support for Spark and the sparklyr package, including tools for:

Creating and managing Spark connections
Browsing the tables and columns of Spark DataFrames
Previewing the first 1,000 rows of Spark DataFrames

Once you<u+2019>ve installed the sparklyr package, you should find a new Spark pane within the IDE. This pane includes a New Connection dialog which can be used to make connections to local or remote Spark instances:

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Once you<u+2019>ve connected to Spark you<u+2019>ll be able to browse the tables contained within the Spark cluster:

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The Spark DataFrame preview uses the standard RStudio data viewer:

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The RStudio IDE features for sparklyr are available now as part of the RStudio Preview Release.

Using H2O

rsparkling is a CRAN package from H2O that extends sparklyr to provide an interface into Sparkling Water. For instance, the following example installs, configures and runs h2o.glm:

options(rsparkling.sparklingwater.version = "1.6.8")

library(rsparkling)
library(sparklyr)
library(dplyr)
library(h2o)

sc <- spark_connect(master = "local", version = "1.6.2")
mtcars_tbl <- copy_to(sc, mtcars, "mtcars")

mtcars_h2o <- as_h2o_frame(sc, mtcars_tbl, strict_version_check = FALSE)

mtcars_glm <- h2o.glm(x = c("wt", "cyl"), 
                      y = "mpg",
                      training_frame = mtcars_h2o,
                      lambda_search = TRUE)

mtcars_glm

## Model Details:
## ==============
## 
## H2ORegressionModel: glm
## Model ID:  GLM_model_R_1486164877174_1 
## GLM Model: summary
##     family     link                              regularization
## 1 gaussian identity Elastic Net (alpha = 0.5, lambda = 0.1013 )
##                                                                lambda_search
## 1 nlambda = 100, lambda.max = 10.132, lambda.min = 0.1013, lambda.1se = -1.0
##   number_of_predictors_total number_of_active_predictors
## 1                          2                           2
##   number_of_iterations training_frame
## 1                    0   frame_rdd_33
## 
## Coefficients: glm coefficients
##       names coefficients standardized_coefficients
## 1 Intercept    38.941654                 20.090625
## 2       cyl    -1.468783                 -2.623132
## 3        wt    -3.034558                 -2.969186
## 
## H2ORegressionMetrics: glm
## ** Reported on training data. **
## 
## MSE:  6.017684
## RMSE:  2.453097
## MAE:  1.940985
## RMSLE:  0.1114801
## Mean Residual Deviance :  6.017684
## R^2 :  0.8289895
## Null Deviance :1126.047
## Null D.o.F. :31
## Residual Deviance :192.5659
## Residual D.o.F. :29
## AIC :156.2425

spark_disconnect(sc)

Connecting through Livy

Livy enables remote connections to Apache Spark clusters. Connecting to Spark clusters through Livy is under experimental development in sparklyr. Please post any feedback or questions as a GitHub issue as needed.

Before connecting to Livy, you will need the connection information to an existing service running Livy. Otherwise, to test livy in your local environment, you can install it and run it locally as follows:

livy_install()

livy_service_start()

To connect, use the Livy service address as master and method = "livy" in spark_connect. Once connection completes, use sparklyr as usual, for instance:

sc <- spark_connect(master = "http://localhost:8998", method = "livy")
copy_to(sc, iris)

## Source:   query [150 x 5]
## Database: spark connection master=http://localhost:8998 app= local=FALSE
## 
##    Sepal_Length Sepal_Width Petal_Length Petal_Width Species
##           <dbl>       <dbl>        <dbl>       <dbl>   <chr>
## 1           5.1         3.5          1.4         0.2  setosa
## 2           4.9         3.0          1.4         0.2  setosa
## 3           4.7         3.2          1.3         0.2  setosa
## 4           4.6         3.1          1.5         0.2  setosa
## 5           5.0         3.6          1.4         0.2  setosa
## 6           5.4         3.9          1.7         0.4  setosa
## 7           4.6         3.4          1.4         0.3  setosa
## 8           5.0         3.4          1.5         0.2  setosa
## 9           4.4         2.9          1.4         0.2  setosa
## 10          4.9         3.1          1.5         0.1  setosa
## # ... with 140 more rows

spark_disconnect(sc)

Once you are done using livy locally, you should stop this service with:

livy_service_stop()

To connect to remote livy clusters that support basic authentication connect as:

config <- livy_config_auth("<username>", "<password">)
sc <- spark_connect(master = "<address>", method = "livy", config = config)
spark_disconnect(sc)