如何从Cassandra用R读取数据？ [英] How to read data from Cassandra with R?

问题描述

我使用R 2.14.1和Cassandra 1.2.11，我有一个单独的程序，它将数据写入单个Cassandra表。

I am using R 2.14.1 and Cassandra 1.2.11, I have a separate program which has written data to a single Cassandra table. I am failing to read them from R.

Cassandra模式定义如下：

The Cassandra schema is defined like this:

create table chosen_samples (id bigint , temperature double, primary key(id))

我已经尝试过RCassandra软件包（ http://www.rforge.net/RCassandra/ ）

I have first tried the RCassandra package (http://www.rforge.net/RCassandra/)

> # install.packages("RCassandra")
> library(RCassandra)
> rc <- RC.connect(host ="192.168.33.10", port = 9160L)
> RC.use(rc, "poc1_samples")
> cs <- RC.read.table(rc, c.family="chosen_samples")

连接似乎成功，但是将表解析为数据框失败：

The connection seems to succeed but the parsing of the table into data frame fails:

> cs
Error in data.frame(..dfd. = c("@\"ffffff", "@(<cc><cc><cc><cc><cc><cd>",  : 
  duplicate row.names: 

连接器，如下所示： http://www.datastax.com/ dev / blog / big-analytics-with-r-cassandra-and-hive

> # install.packages("RJDBC")
> library(RJDBC)
> cassdrv <- JDBC("org.apache.cassandra.cql.jdbc.CassandraDriver", "/Users/svend/dev/libs/cassandra-jdbc-1.2.5.jar", "`")

像这样：

Error in .jfindClass(as.character(driverClass)[1]) : class not found

即使java驱动程序的位置是正确的

Even though the location to the java driver is correct

$ ls /Users/svend/dev/libs/cassandra-jdbc-1.2.5.jar
/Users/svend/dev/libs/cassandra-jdbc-1.2.5.jar

推荐答案

您必须下载 apache-cassandra-2.0。 10-bin.tar.gz 和 cassandra-jdbc-1.2.5.jar 和 cassandra-all-1.1.0.jar 。

不需要在本地机器上安装Cassandra;只需将cassandra-jdbc-1.2.5.jar和cassandra-all-1.1.0.jar文件放在解压缩的apache-cassandra-2.0.10-bin.tar.gz的lib目录中。然后您可以使用

There is no need to install Cassandra on your local machine; just put the cassandra-jdbc-1.2.5.jar and the cassandra-all-1.1.0.jar files in the lib directory of unziped apache-cassandra-2.0.10-bin.tar.gz. Then you can use

 library(RJDBC)
 drv <- JDBC("org.apache.cassandra.cql.jdbc.CassandraDriver", 
              list.files("D:/apache-cassandra-2.0.10/lib",
              pattern="jar$",full.names=T))

这是在我的unix，但不是在我的Windows机器上。
希望有帮助。

That is working on my unix but not on my windows machine. Hope that helps.

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