Spark >= 1.5
从Spark 1.5开始,您可以按如下方式解析日期字符串:
from pyspark.sql.functions import expr, from_unixtime, lit, unix_timestamp
from pyspark.sql.types import TimestampType
parsed_df = df.select((from_unixtime(unix_timestamp(
df.datetime, "dd-MMM-yy h.mm.ss.SSSSSS a"
))).cast(TimestampType()).alias("datetime"))
parsed_df.where(col("datetime") >= lit(now) - expr("INTERVAL 5 minutes"))
然后应用间隔:
from pyspark.sql.functions import current_timestamp, expr
Spark < 1.5
可以使用用户定义的函数。
from datetime import datetime, timedelta
from pyspark.sql.types import BooleanType, TimestampType
from pyspark.sql.functions import udf, col
def in_last_5_minutes(now):
def _in_last_5_minutes(then):
then_parsed = datetime.strptime(then, '%d-%b-%y %I.%M.%S.%f %p')
return then_parsed > now - timedelta(minutes=5)
return udf(_in_last_5_minutes, BooleanType())
使用一些虚拟数据:
df = sqlContext.createDataFrame([
(1, '14-Jul-15 11.34.29.000000 AM'),
(2, '14-Jul-15 11.34.27.000000 AM'),
(3, '14-Jul-15 11.32.11.000000 AM'),
(4, '14-Jul-15 11.29.00.000000 AM'),
(5, '14-Jul-15 11.28.29.000000 AM')
], ('id', 'datetime'))
now = datetime(2015, 7, 14, 11, 35)
df.where(in_last_5_minutes(now)(col("datetime"))).show()
如预期,我们只得到3个条目:
+--+--------------------+
|id| datetime|
+--+--------------------+
| 1|14-Jul-15 11.34.2...|
| 2|14-Jul-15 11.34.2...|
| 3|14-Jul-15 11.32.1...|
+--+--------------------+
重复解析日期时间字符串的效率较低,因此您可以考虑存储 TimestampType
。
def parse_dt():
def _parse(dt):
return datetime.strptime(dt, '%d-%b-%y %I.%M.%S.%f %p')
return udf(_parse, TimestampType())
df_with_timestamp = df.withColumn("timestamp", parse_dt()(df.datetime))
def in_last_5_minutes(now):
def _in_last_5_minutes(then):
return then > now - timedelta(minutes=5)
return udf(_in_last_5_minutes, BooleanType())
df_with_timestamp.where(in_last_5_minutes(now)(col("timestamp")))
结果如下:
+--+--------------------+--------------------+
|id| datetime| timestamp|
+--+--------------------+--------------------+
| 1|14-Jul-15 11.34.2...|2015-07-14 11:34:...|
| 2|14-Jul-15 11.34.2...|2015-07-14 11:34:...|
| 3|14-Jul-15 11.32.1...|2015-07-14 11:32:...|
+--+--------------------+--------------------+
现在可以使用时间戳来进行原始SQL查询:
query = """SELECT * FROM df
WHERE unix_timestamp(datetime, 'dd-MMM-yy HH.mm.ss.SSSSSS a') > {0}
""".format(time.mktime((now - timedelta(minutes=5)).timetuple()))
sqlContext.sql(query)
和上面一样,解析日期字符串一次会更有效率。
如果列已经是时间戳timestamp
类型,可以使用datetime
字面值:
from pyspark.sql.functions import lit
df_with_timestamp.where(
df_with_timestamp.timestamp > lit(now - timedelta(minutes=5)))