如何在sparklyr中按名称引用Spark DataFrame并将其分配给变量? [英] How to refer to a Spark DataFrame by name in sparklyr and assign it to a variable?
问题描述
说我运行了以下代码,但我忘记了将Spark数据帧 iris
分配给R中的变量,我不能使用。 .value
进行分配,因为我在将数据复制到Spark后立即运行了一些其他代码。
Say I ran the following code and I forgot to assign the Spark dataframe iris
to a variable in R and I can't use .Last.value
to assign because I had run some other code right after copying the data to Spark.
library(sparklyr)
library(dplyr)
sc <- spark_connect(master = "local")
copy_to(sc, iris)
2+2 # ran some other code so can't use .Last.value
如何将Spark数据帧 iris附加到R中的变量称为 iris_tbl
?
How do I assing the Spark dataframe "iris" to a variable in R called iris_tbl
?
推荐答案
copy_to
提供其他 name
参数默认情况下,它设置为:
copy_to
provides additional name
argument By default it is set to:
deparse(substitute(df))
所以在您的情况下,名称为 iris
。如果您想要更可预测的行为,则应该手动设置名称:
so in your case the name will be iris
. If you want more predictable behavior you should set the name manually:
copy_to(sc, iris, name = "foo")
然后,您可以通过<< c $ c> dplyr code> tbl :
Then you can access it dplyr
way with tbl
:
dplyr::tbl(sc, "foo")
或通过Spark会话:
or via Spark session:
sc %>% spark_session() %>% invoke("table", "foo") %>% sdf_register()
所有可用于生产环境的读取器方法( copy_to
不应用作测试和开发工具,而只能用作其他工具)需要 name
,因此您可以用相同的方式引用表
All production ready reader methods (copy_to
shouldn't be used as anything else than a testing and development tool) require name
, so you can reference tables the same way
spark_read_csv(sc, "bar", path)
tbl(sc, "bar")
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