将字符串转换为datetime在SparkR？

问题描述

我有一个是（通过一个JSON文件）上传到SparkR从MySQL正式上课数据框对象，其中包含格式的字符串是这样的：
    2012-07-02 20点14分○○秒

I have a Formal Class DataFrame object that was uploaded to SparkR from MySQL (via a json file), which contains formatted strings like this: "2012-07-02 20:14:00"

我需要把这些转换为SparkR日期时间类型，但这似乎并不能被支持。是否有一个未公开的函数或者用UDF这样的食谱？ （注意，我并​​没有真正尝试过创建SparkR UDF，所以我抓救命稻草，在这里。）

I need to convert these to a datetime type in SparkR, but this does not seem to be supported yet. Is there an undocumented function or a recipe for doing this with a UDF? (Nb. I haven't actually tried creating a SparkR UDF before, so I'm grasping at straws, here.)

推荐答案

星火SQL不支持研究的UDF但在这种特殊情况下你可以简单地转换为时间戳：

Spark SQL doesn't support R UDFs but in this particular case you can simply cast to timestamp:

df <- createDataFrame(sqlContext, 
  data.frame(dts=c("2012-07-02 20:14:00", "2015-12-28 00:10:00")))
dfWithTimestamp <- withColumn(df, "ts", cast(df$dts, "timestamp"))

printSchema(dfWithTimestamp)
## root
##  |-- dts: string (nullable = true)
##  |-- ts: timestamp (nullable = true)

head(dfWithTimestamp)
##                   dts                  ts
## 1 2012-07-02 20:14:00 2012-07-02 20:14:00
## 2 2015-12-28 00:10:00 2015-12-28 00:10:00

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