How to change the column type from String to Date

问题:

I have a dataframe that have two columns (C, D) are defined as string column type, but the data in the columns are actually dates. for example column C has the date as "01-APR-2015" and column D as "20150401" I want to change these to date column type, but I didn't find a good way of doing that. I look at the stack overflow I need to convert the string column type to Date column type in Spark SQL's DataFrame. the date format can be "01-APR-2015" and I look at this post but it didn't have info relate to date

回答1:

Spark >= 2.2

You can use to_date:

import org.apache.spark.sql.functions.{to_date, to_timestamp}

df.select(to_date($"ts", "dd-MMM-yyyy").alias("date"))

or to_timestamp:

df.select(to_date($"ts", "dd-MMM-yyyy").alias("timestamp"))

with intermediate unix_timestamp call.

Spark < 2.2

Since Spark 1.5 you can use unix_timestamp function to parse string to long, cast it to timestamp and truncate to_date:

import org.apache.spark.sql.functions.{unix_timestamp, to_date}

val df = Seq((1L, "01-APR-2015")).toDF("id", "ts")

df.select(to_date(unix_timestamp(
  $"ts", "dd-MMM-yyyy"
).cast("timestamp")).alias("timestamp"))

Note:

Depending on a Spark version you this may require some adjustments due to SPARK-11724:

Casting from integer types to timestamp treats the source int as being in millis. Casting from timestamp to integer types creates the result in seconds.

If you use unpatched version unix_timestamp output requires multiplication by 1000.